To examine circumstances surrounding suboptimally timed retinal photocoagulation, we reviewed the medical records of 238 patients who had received photocoagulation for diabetic retinopathy at one of three large referral centers. Forty-three percent (95% confidence interval, 36% to 49%) of cases were rated as probably or definitely sub-optimally timed (i.e., patient could have benefited from earlier photocoagulation). About one third of cases were due to patients going many years without screening (>3 years), and two thirds were associated with surveillance problems (failure to achieve close follow-up for known retinopathy). We found that suboptimal timing of photocoagulation was common but was not due to patients going between 13 and 36 months between screening visits, suggesting that current performance measures, which focus on annual retinal examinations, may be requiring wasteful care while not addressing a major quality problem.