We reviewed the records of 18 patients with persistent esotropia after maximal recession of each medial rectus muscle on whom marginal myotomy of both medial recti muscles was subsequently performed. We compared the results in patients with essential infantile esotropia, acquired esotropia, nonaccommodative convergence excess, and nystagmus compensation syndrome. After a follow-up of three years, the mean improvement of esotropia at distance fixation was 9 prism diopters (range, -20 to +41 prism diopters) and was 21 prism diopters at near fixation (range, +4 to +50 prism diopters). The effect of marginal myotomy of previously maximally recessed medial recti muscles is unpredictable. However, we believe it to be an acceptable secondary surgical procedure in selected cases of persistent esotropia. The best results were obtained in essential infantile esotropia.