The incidence, severity, and duration of ptosis after botulinum neurotoxin type A (BAT) injections into extraocular or orbicularis muscles were reviewed retrospectively. Even though lid droop frequently complicated botulinum toxin treatment in this series, no loss of vision or permanent ptosis was encountered. Sixty-seven injections were completed in 44 patients between September 1982 and December 1983. The records were reviewed to determine the incidence of ptosis after these 67 injections. Information was not adequate to ascertain the presence or absence of ptosis after 10 injections. Some degree of ptosis developed after 30 (53%) of the 57 injections with adequate follow-up history. Marked ptosis occurred after 12 (21%) of the 57 injections. The posttreatment lid droop in these 12 cases was potentially visually significant. All cases of ptosis, which impinged on the visual axis, resolved to a level permitting undisturbed vision by eight weeks after toxin injection. The incidence of ptosis was similar in patients who received injections into their medial rectus muscles and in patients who received injections into their lateral rectus muscles. However, an increased incidence of marked ptosis may be associated with the injection of previously operated muscles. Toxin dosage, patient age, and quality of the electromyogram used to monitor the injection showed no statistically significant relationship to the ptosis.