Objectives. To examine the relationship between diabetes-specific health locus of control patterns and metabolic control (HbA1C). The validity and reliability of the Diabetes Locus of Control Scale (DLOC) used were also examined. Methods. Study participants were 312 consecutive adult Swedish out-patients with insulin-dependent diabetes mellitus (IDDM). The participants completed the DLOC at their regular clinic visit and data on metabolic control (HbA1C) and background factors were gathered. Results. The Diabetes Locus of Control Scale was found to have adequate psychometric properties. Participants with strong beliefs that their own behaviour is responsible for the course of the disease and weak beliefs in chance and luck were metabolically better regulated than participants who exhibited other health locus of control patterns. Conclusions. The diabetes locus of control patterns examined appear to have explanatory power in accounting for metabolic control. The data suggest that, in planning treatment of IDDM patients, clinicians could make use of knowledge concerning the patients' health locus of control patterns.