Case records of patients who had macular detachment following argon laser photocoagulation for proliferative diabetic retinopathy were reviewed. Thirteen eyes of 11 patients out of a total of 480 patients treated had this complication, and in 12 eyes of 10 patients the short latency suggested a true precipitating effect. This represents 2.1% of patients receiving panretinal photocoagulation. Patients with detachment were younger and developed diabetes earlier than the controls (P less than 0.025), and the detached eyes had received more numerous laser burns on average per session than the controls (P less than 0.001). In 5 eyes the last photocoagulation dose exceeded 1000 burns delivered in the presence of traction membranes in an attempt to arrest continuing neovascular proliferation not responding to earlier more moderate treatment. Only 1 eye had received early, extensive and repeated photocoagulation. Vigorous treatment at an early stage of the proliferation may prevent this complication, although the advantages or disadvantages of fractionation of photocoagulation will only be shown by a prospective trial.