A retrospective and prospective study of 1,000 ambulatory and hospitalized diabetic patients was done in Riyadh, Saudi Arabia. Saudis comprised 777 (77.7%) and non-Saudis 223 (22.3%). Sex distribution was equal among Saudis, males 389 (50.1%) and females 388 (49.9%), but non-Saudi males were predominant at 153 (68.6%), nonSaudi females 70 (31.4%) reflecting the preponderant male expatriate labor force. A proportion of different types of diabetes was: IDDM115 (11.7%), non-obese non-insulin dependent diabetes mellitus (NIDDM) 405 (41.0%), obese NIDDM 412 (42.1%), and early onset non-insulin dependent diabetes (diagnosis under 30 years of age), 43 (4.4%). Regarding treatment, 388 (40.6%) received insulin followed by sulfonylurea, alone in 330 (33.5%), diet only in 117 (12.0%), combination sulfonylurea and biguanide in 113 (11.6%), biguanide alone in 13 (1.3%) and insulin plus tablets in 7 (0.8%). Of 472 and 426 patients, 29.7% and 30.0% had elevated total cholesterol or triglycerides respectively, while 77.2% of 373 patients had elevated glycosylated hemoglobin (HbAl). At least once in 998 patients, diabetic ketoacidosis occurred in 7.6%,hypoglycemia (BS ≤ 2.2 mmols/1) in 8.6% and severe hyperglycemia (blood sugar ≥ 27.7 mmols/1) in 16.5%. The frequency of chronic and infective complications was: cataract 42.7%, infection 37.9%, neuropathy 35.9%, retinopathy 31.5%, hypertension 25.6%, nephropathy 17.8%, ischemic heart disease 11.3%, foot lesions 10.5%, stroke 9.4%, renal insufficiency 6.9% and amputation 5.1%. The pattern of diabetes in Saudi Arabia is similar to that in other countries, but the occurrence of early onset NIDDM and the role of consanguinity need clarification. Tropical pancreatic diabetes is rare. The spectrum of complications is a combination of what is observed in developing as well as industrialized countries.