OBJECTIVES: To identify prescription patterns for diabetes treatment among a group of individuals covered by Colombia's universal health care, the General System for Social Security in Health (SGSSS). METHODS: The study included 7 308 patients covered by SGSSS who had diabetes mellitus type 1 or 2, were of either sex, any age, and had been undergoing treatment for at least three months (May-July 2005) in 19 cities in Colombia. A database was compiled from the medication usage records maintained by the dispensing pharmacy. Data were analyzed using SPSS 13.0 (SPSS Inc., Chicago, Illinois, United States of America). Student's t-test and analysis of variance (ANOVA) were employed to compare quantitative variables, and the chi-square test was applied to compare categorical variables. RESULTS: The patients' mean age was 60.7 +/- 12.7 years. Women made up 56.6% of the group and had a mean age significantly higher than that of the men (P < 0.05). Forty-eight percent of the group had been prescribed one diabetes medication, while 52% had been prescribed from two to four. The medications prescribed were: biguanides (67.5%), sulphonylureas (64.9%), insulin (23.5%), and thiazolidinediones (0.1%). The most common oral combination-therapies were: glibenclamide and metformin (n = 2 847), metformin and insulin (n = 510), glibenclamide and insulin (n = 148), and metformin, insulin, and glibenclamide (n = 288). Of the total, 94.3% had comorbid conditions for which they had been prescribed medication: antihypertensive drugs (in 74.4% of the cases), anti-inflammatories (61.5%), hypolipemiants (45.5%), antiulcer medications (21.0%), psychoactive drugs (16.8%), antimicrobials (14.4%), asthma medication (5.3%), and salicylic acid (2.8%). Prescriptions for comorbid conditions were more common among women than men (95.6% vs. 92.7%, P < 0.001). Undertreatment with certain medications (metformin, thiazolidinediones, alpha-glucosidase inhibitors, and salicylic acid), and overtreatment with others (antiulcer drugs), probably exist. CONCLUSIONS: There are significant differences in oral therapies prescribed for diabetes across the 19 cities studied, but overall, prescription patterns are appropriate. Educational strategies should be developed to address those prescribing practices that are not appropriate, and the clinical results of the medications studied should be explored.