Studies of temperament profiles in patients with mental disorders mostly focus on emotionality-related traits, although mental illness symptoms include emotional and nonemotional aspects of behavioral regulation. This study investigates relationships between 12 temperament traits (9 nonemotionality and 3 emotionality related) measured by the Structure of Temperament Questionnaire and four groups of clinical symptoms (depression, anxiety, antisociality, and dominance-mania) measured by the Personality Assessment Inventory. The study further examines age differences in relationships among clinical symptoms and temperament traits. Intake records of 335 outpatients and clients divided into four age groups (18–25, 26–45, 46–65, and 66–85) showed no significant age differences on depression scales; however, the youngest group had significantly higher scores on Anxiety, Antisocial Behavior, Dominance, and Thought Disorders scales. Correlations between Personality Assessment Inventory and Structure of Temperament Questionnaire scales were consistent with Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, descriptors showing strong concurrent validity. Several age differences on temperament scales are also reported. Results show the benefits of differentiation between physical, social-verbal, and mental aspects of activities, as well as differentiation between dynamical, orientational, and energetic aspects in studying mental illness and temperament.