Many researchers and theorists and argued that a person's psychological health and well-being require that needs are met. If needs are not met, the result is distress and attempts to compensate, both of which may lead to psychological problems. Thus, psychologists and others whose goal is to help people with psychological problems require a theory of important psychological needs.This study provides a critical review of major need theories and assessment instruments developed to operationalize those theories. Based upon this review, five needs (autonomy, competence, relatedness, purpose, and physical) were identified as being critical aspects of psychological well-being. Using a relatively new needs assessment scale, these five needs were assessed in 1,358 clinical and non-clinical adults from various sites around a Midwestern state.Results indicated a five-factor structure that was slightly different than the one originally hypothesized. This new five factor model (life direction, positive interpersonal relations, interpersonal support, competence, and ability to adapt) was found to be consistent across both the clinical and non-clinical samples. Results provided strong evidence that the measurement instrument has superior psychometric properties to previously developed instruments. Importantly, this new need assessment inventory could discriminate clinical from non-clinical samples. An additional important finding concerned self-esteem. Many researchers have argued about whether self-esteem is a need. Results here suggest that self-esteem is not a need, but is either irrelevant or may be a vague measure of several needs. Suggestions for future research and implications for clinical treatment are discussed. / Department of Psychological Science