diff --git a/error.go b/error.go
index bdd49c3..b974460 100644
--- a/error.go
+++ b/error.go
@@ -5,9 +5,13 @@ import (
 	"os"
 )
 
+func PrintToStderr(v interface{}) {
+	fmt.Fprintf(os.Stderr, "%v: %v\n", os.Args[0], v)
+}
+
 func ExitIfError(err error) {
 	if err != nil {
-		fmt.Fprintf(os.Stderr, "%v: %v\n", os.Args[0], err)
+		PrintToStderr(err)
 		os.Exit(1)
 	}
 }
diff --git a/md5sum/md5sum.go b/md5sum/md5sum.go
new file mode 100644
index 0000000..6d5d1aa
--- /dev/null
+++ b/md5sum/md5sum.go
@@ -0,0 +1,141 @@
+package main
+
+import (
+	"bufio"
+	"crypto/md5"
+	"errors"
+	"fmt"
+	"hash"
+	"io"
+	"os"
+	"strings"
+
+	"github.com/alexflint/go-arg"
+	common "source.heropunch.io/tomo/go-coreutils"
+)
+
+var ImproperlyFormattedErr = errors.New("improperly formatted line")
+
+func printSumForFile(filename string, sumFunc func(io.Reader) (hash.Hash, error)) error {
+	file, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	h, err := sumFunc(file)
+	if err != nil {
+		return err
+	}
+
+	printHash(h, filename)
+	return nil
+}
+
+func printSumForStdin(sumFunc func(io.Reader) (hash.Hash, error)) {
+	h, err := sumFunc(os.Stdin)
+	if err != nil {
+		common.PrintToStderr(err)
+		os.Exit(1)
+	}
+	printHash(h, "<stdin>")
+	os.Exit(0)
+}
+
+func md5sum(r io.Reader) (hash.Hash, error) {
+	h := md5.New()
+	if _, err := io.Copy(h, r); err != nil {
+		return nil, err
+	}
+	return h, nil
+}
+
+func printHash(h hash.Hash, filename string) {
+	fmt.Printf("%x  %v\n", h.Sum(nil), filename)
+}
+
+func checkSumForFile(filename string) error {
+	file, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	return checkSums(file)
+}
+
+func checkSums(r io.Reader) error {
+	scanner := bufio.NewScanner(r)
+
+	for scanner.Scan() {
+		err := checkMD5Sum(scanner.Text())
+		if err != nil {
+			return err
+		}
+	}
+	return scanner.Err()
+}
+
+func checkMD5Sum(line string) error {
+	s := strings.SplitN(line, "  ", 2)
+	hash := s[0]
+	filename := s[1]
+
+	if filename == "" {
+		return ImproperlyFormattedErr
+	}
+
+	file, err := os.Open(filename)
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	h, err := md5sum(file)
+	if err != nil {
+		return err
+	}
+	result := "OK"
+	if fmt.Sprintf("%x", h.Sum(nil)) != hash {
+		result = "FAILED"
+	}
+	fmt.Printf("%s: %s\n", filename, result)
+
+	return nil
+}
+
+func main() {
+	var args struct {
+		Check bool     `arg:"-c"`
+		Files []string `arg:"positional"`
+	}
+
+	arg.MustParse(&args)
+
+	exitCode := 0
+	if len(args.Files) == 0 {
+		if !args.Check {
+			printSumForStdin(md5sum)
+		} else {
+			fmt.Println("Checking from stdin")
+		}
+	}
+
+	for _, filename := range args.Files {
+		if !args.Check {
+			err := printSumForFile(filename, md5sum)
+			if err != nil {
+				common.PrintToStderr(err)
+				exitCode = 1
+			}
+		} else {
+			err := checkSumForFile(filename)
+			if err != nil {
+				common.PrintToStderr(err)
+				exitCode = 1
+			}
+		}
+	}
+
+	os.Exit(exitCode)
+}