The Developmental Profile is an instrument for personality assessment. It covers both maladaptive and adaptive characteristics. The current study examined its internal consistency and construct validity in a Dutch sample of 763 participants from various clinical and nonclinical settings. The internal consistency reliability estimates were good for the clusters of levels (adaptive, neurotic, and primitive), although not for all separate levels. Confirmatory factor analysis showed an overall good fit, with the exception of the level of primary narcissism. Furthermore, empirical evidence was found for the interpretation of a patient's Developmental Profile according to increasing levels of aggregation, with as a highest level a single maladaptivity-adaptivity scale score. This scale significantly distinguished among different patient groups.