This study assessed the construct validity of the circumplex model of the Inventory of Interpersonal Problems (IIP-C) in Norwegian clinical and nonclinical samples. Structure was examined by evaluating the fit of the circumplex model to data obtained by the IIP-C. Observer-rated personality disorder criteria (DSM-IV, Axis II) were used as external correlates. The reliability of the IIP-C scales was acceptable and in the same range as in the original version. A multisample analysis strategy did not support an invariant circumplex model across the 2 groups. However, the estimated structures reflected mostly the same circular pattern of a quasi-circumplex model in the 2 groups. Departures from the ideal model were of negligible practical significance. The validity results examining personality disorder correlates of the IIP-C generally conformed to predictions, providing direct evidence for agreement between self-report and expert judgments of interpersonal problems.