The aim of this study was to analyse the response of a cohort of patients with convergence spasm to the injection of botulinum toxin (BT) in the medial rectus muscle. This was a retrospective study of six patients with a mean age of 44.3 years. The patients complained of diplopia, headaches and blurred vision and had variable esotropia measuring on average 32.5PD at near and 27.7PD at distance pre BT. Five had previous treatment with atropine drops and plus lenses. One had prisms. At two weeks post BT, four were over corrected by an average 10PD exotropia at near and 8.3PD at distance. Two had transient ptosis. At three months post BT the average angle was 12.5PD esotropia at near and 9.1PD at distance. At final follow-up, all had regressed to convergence spasm. In their cohort, BT was found to be of limited success.