Development and initial validation of the FACES of fatigue and sleepiness adjective checklist. An initial item pool of 65 adjectives, descriptive of fatigue, sleepiness and related deprivation states, was developed and administered to 372 individuals referred by their family physicians for psychiatric investigation and treatment of severe insomnia. Participants attended one of six Canadian university-affiliated sleep clinics where they completed a psychiatric assessment and a 766-item questionnaire, including a number of standard indices of sleep-related behavior and symptoms, medical history, sleep hygiene, psychosocial well-being and psychopathology. Principal-components and item analyses were undertaken to refine the initial 65-item pool to a smaller 50-item set, consisting of five subscales: Fatigue, Anergy, Consciousness, Energized and Sleepiness. Coefficient alpha was calculated and indicated high internal consistency reliability for all subscales. Convergent and discriminant validity were also evaluated by calculating correlations between FACES subscales and a number of independent indices. The resulting five-scale FACES questionnaire appears to offer a promising self-report instrument for the measurement of fatigue and related subjective experiences.