Clinical decision-making in mental health could greatly benefit from evidence-based decision tools, particularly in diagnosing challenging, high-stakes conditions such as pediatric bipolar disorder. The current literature indicates that clinicians are prone to a host of cognitive biases that impede optimal diagnostic and treatment decisions. These biases are especially salient in the assessment of bipolar illness. Bipolar disorder is frequently misdiagnosed, and recent evidence suggests that mental health professionals often overdiagnose bipolar in youths. Although actuarial approaches have taken root in the medical community to assess the likelihood of various conditions, the mental health field has not widely disseminated or implemented such strategies. In fact, little research has attempted to validate the clinical utility of actuarial assessment methods. This study examines the effectiveness of an actuarial approach in diagnosing pediatric bipolar disorder by comparing Bayesian estimates (i.e., actuarial approach) to the current gold standard in clinical assessment.