diff --git a/tools/osv-linter/internal/pkgchecker/ecosystems.go b/tools/osv-linter/internal/pkgchecker/ecosystems.go
index 7152dce..7e6f532 100644
--- a/tools/osv-linter/internal/pkgchecker/ecosystems.go
+++ b/tools/osv-linter/internal/pkgchecker/ecosystems.go
@@ -155,7 +155,7 @@ func VersionsExistInEcosystem(pkg string, versions []string, ecosystem string) e
 	case "MinimOS":
 		return nil
 	case "npm":
-		return nil
+		return versionsExistInNpm(pkg, versions)
 	case "NuGet":
 		return nil
 	case "openSUSE":
diff --git a/tools/osv-linter/internal/pkgchecker/ecosystems_test.go b/tools/osv-linter/internal/pkgchecker/ecosystems_test.go
index 4eba81a..f907a07 100644
--- a/tools/osv-linter/internal/pkgchecker/ecosystems_test.go
+++ b/tools/osv-linter/internal/pkgchecker/ecosystems_test.go
@@ -38,6 +38,70 @@ func Test_versionsExistInGo(t *testing.T) {
 	}
 }
 
+func Test_versionsExistInNpm(t *testing.T) {
+	t.Parallel()
+
+	type args struct {
+		pkg      string
+		versions []string
+	}
+	tests := []struct {
+		name    string
+		args    args
+		wantErr bool
+	}{
+		{
+			name: "multiple_versions_which_all_exist",
+			args: args{
+				pkg:      "semver",
+				versions: []string{"1.0.1", "2.0.0-beta", "5.7.1"},
+			},
+			wantErr: false,
+		},
+		{
+			name: "multiple_versions_with_one_that_does_not_exist",
+			args: args{
+				pkg:      "semver",
+				versions: []string{"1.1", "2.0.0-beta1", "3.1.5", "5.1rc1"},
+			},
+			wantErr: true,
+		},
+		{
+			name: "an_invalid_version",
+			args: args{
+				pkg:      "semver",
+				versions: []string{"!"},
+			},
+			wantErr: true,
+		},
+		{
+			name: "an_invalid_package",
+			args: args{
+				pkg:      "!",
+				versions: []string{"1.0.0"},
+			},
+			wantErr: true,
+		},
+		{
+			name: "a_package_that_does_not_exit",
+			args: args{
+				pkg:      "not-a-real-package-hopefully",
+				versions: []string{"1.0.0"},
+			},
+			wantErr: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			if err := versionsExistInNpm(tt.args.pkg, tt.args.versions); (err != nil) != tt.wantErr {
+				t.Errorf("versionsExistInNpm() error = %v, wantErr %v", err, tt.wantErr)
+			}
+		})
+	}
+}
+
 func Test_versionsExistInPackagist(t *testing.T) {
 	t.Parallel()
 
diff --git a/tools/osv-linter/internal/pkgchecker/version_check.go b/tools/osv-linter/internal/pkgchecker/version_check.go
index 227ada2..5645c0f 100644
--- a/tools/osv-linter/internal/pkgchecker/version_check.go
+++ b/tools/osv-linter/internal/pkgchecker/version_check.go
@@ -129,6 +129,58 @@ func goVersionsExist(versions []string) error {
 	return nil
 }
 
+// Confirm that all specified versions of a package exist in npm.
+func versionsExistInNpm(pkg string, versions []string) error {
+	packageInstanceURL := fmt.Sprintf("%s/%s", EcosystemBaseURLs["npm"], pkg)
+
+	resp, err := faulttolerant.Get(packageInstanceURL)
+	if err != nil {
+		return fmt.Errorf("unable to validate package: %v", err)
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return fmt.Errorf("unable to validate package: %q for %s", resp.Status, packageInstanceURL)
+	}
+
+	// Parse the known versions from the JSON.
+	respJSON, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return fmt.Errorf("unable to retrieve JSON for %q: %v", pkg, err)
+	}
+	// Fetch all known versions of package.
+	versionsInRepository := []string{}
+	releases := gjson.GetBytes(respJSON, "versions.@keys")
+	releases.ForEach(func(key, value gjson.Result) bool {
+		versionsInRepository = append(versionsInRepository, value.String())
+		return true // keep iterating.
+	})
+	// Determine which referenced versions are missing.
+	versionsMissing := []string{}
+	for _, versionToCheckFor := range versions {
+		versionFound := false
+		vc, err := semantic.Parse(versionToCheckFor, "npm")
+		if err != nil {
+			versionsMissing = append(versionsMissing, versionToCheckFor)
+			continue
+		}
+		for _, pkgversion := range versionsInRepository {
+			if r, err := vc.CompareStr(pkgversion); r == 0 && err == nil {
+				versionFound = true
+				break
+			}
+		}
+		if versionFound {
+			continue
+		}
+		versionsMissing = append(versionsMissing, versionToCheckFor)
+	}
+	if len(versionsMissing) > 0 {
+		return &MissingVersionsError{Package: pkg, Ecosystem: "npm", Missing: versionsMissing, Known: versionsInRepository}
+	}
+
+	return nil
+}
+
 // Confirm that all specified versions of a package exist in Packagist.
 func versionsExistInPackagist(pkg string, versions []string) error {
 	packageInstanceURL := fmt.Sprintf("%s/%s.json", EcosystemBaseURLs["Packagist"], pkg)