Nonadherence to immunosuppressants in renal transplant recipients is a major factor affecting graft survival, but it is difficult to detect accurately in clinical practice. Adherence was measured in 153 adult renal transplant recipients using self-report questionnaires and interview, clinician rating, and cyclosporine levels. The sensitivity and specificity of these measures were determined by comparison with electronic monitoring in a randomly selected subsample of 58 subjects. Measures of adherence in current clinical use do not perform well when tested against electronic monitoring. Self-report at a confidential interview was the best measure of adherence for the detection of both missed doses and erratic timing of medication. However, the use of a confidential interview is not directly applicable to a clinical setting. Further research on how best to facilitate disclosure in clinical settings may be the best way to develop adherence measures for use in routine practice.