A screening project was established to assess the prevalence and severity of retinopathy in diabetic patients in Tayside (area: 3000 square miles, population: 390,000). A questionnaire was used to examine patient acceptability. Of 2112 patients photographed during the first year, 32% had abnormal photographs; 20.2% had diabetic retinopathy; 7.4% cataracts; 4.6% non-diabetic eye disease. Among this patient population, 73% were registered at a hospital diabetic clinic. The overall prevalence of diabetic retinopathy was similar between the two groups (hospital 23% vs non-hospital 20%). The prevalence of severe diabetic retinopathy was also similar (hospital 8.5% vs non-hospital 10%). This had been previously unrecognized or incorrectly defined in 6.5% of those not attending a hospital diabetic clinic, compared to 3.7% attending the hospital clinic (p less than 0.01). A favourable response to the service was indicated by 40% of patients with 7% unfavourable and 41% uncommitted. Non-mydriatic fundal photography housed in a mobile unit is a practical and effective method of assessing diabetic retinopathy. It is particularly suitable for screening in a widely spread population.