Losing a case was a rarity for Matlock, but he has had the occasion to correct that, as with Lester Matthews (The Convict), when Lester was tried for murdering a fellow inmate. Another one he lost was when Ken Wilson was arrested for killing his wife (The Black Widow).

Does Matlock ever lose a case?

Matlock has virtually never lost a case (see Ethical Issues), and often not only gets his client off but reveals the true guilty party in the process. Although we've only got a sample size of one for Atticus Finch, it's a loss.

How many cases has Matlock?

Though Matlock went on to win every case, he did lose three times, and later had the occasion to correct that.