OBJECTIVE: To examine (1) the 1-year and lifetime prevalence of suicidal thoughts and behavior among adolescents with insulin-dependent diabetes mellitus (IDDM), (2) the relationship between suicidal thoughts and serious noncompliance with the medical regimen, and (3) factors including psychiatric disorder, self-efficacy expectations, and hopelessness that might mediate the relationship between suicidal thoughts and noncompliance. METHOD: Semistructured and structured interview instruments and self-report questionnaires were used to determine history of suicidal thoughts and behavior, serious noncompliance with the medical regimen, current psychiatric disorder, hopelessness, and self-efficacy expectations among 91 adolescents attending outpatient clinic appointments. RESULTS: The rate of suicidal ideation among the diabetic adolescents was higher than expected, but the rate of suicide attempts was comparable with that reported for the general population. Suicidal thoughts were strongly associated with serious noncompliance with the medical regimen. Duration of IDDM and psychiatric diagnosis were related to both suicidal ideation within the previous year and lifetime suicidal ideation. Diagnosable psychiatric disorder and not living in a two-parent home were related to noncompliance with medical treatment. CONCLUSIONS: Suicidal thoughts and serious noncompliance with the medical regimen are strongly associated among diabetic teenagers, and psychiatric disorder is a common correlate of both.