Patients with chronic medical conditions such as diabetes mellitus need to self-manage their condition for optimal outcomes. The degree to which patients with diabetes feel competent or self-efficacious in managing their diabetes has been related to behaviors such as dieting or exercise as well as to indicators of glycemic control. A diabetes-specific adaptation of the Perceived Medical-Condition Self-Management Scale was administered to 398 patients with either type 1 (n=57) or type 2 (n=341) diabetes. Cronbach's alpha of the 8-item Perceived Diabetes Self-Management Scale (PDSMS) was .83 indicating internal consistency. PDSMS scores were uncorrelated with age, years since diagnosis, and years of schooling, but were negatively correlated with body mass index. Those with type 1 DM had higher PDSMS scores than those with type 2 DM. PDSMS scores were positively correlated with a number of self-reported self-care activities and negatively related to measures of glycemic control. The PDSMS is a valid measure of diabetes self-efficacy, and the more generic template from which it was adapted can easily be altered for use with other chronic medical conditions.