Objective: The aim of the study was to understand the relationship between affective temperaments and insomnia symptoms and to examine mood state as a mediator in this relationship. Participants: The sample consisted of 659 adults (428 women and 231 men), aged 18-77 years old, derived from a nonclinical population. Methods: Affective temperaments were assessed using the Temperament Evaluation of Memphis, Pisa, Paris, and San Diego Autoquestionnaire (TEMPS-A). Mood was measured using the UWIST Mood Adjective Checklist (UMACL). Insomnia was evaluated by the Athens Insomnia Scale. Results: We found positive correlations among anxious, cyclothymic, depressive, and irritable affective temperaments and insomnia symptoms. Negative correlation with insomnia symptoms was found for hyperthymic temperament. Energetic arousal and tense arousal, as mood dimensions, positively correlated with insomnia symptoms. Hierarchical regression analysis indicated that anxious, cyclothymic, and hyperthymic temperaments were significant predictors of insomnia symptoms. Mediation analyses indicated that anxious, cyclothymic, and hyperthymic temperaments affected insomnia symptoms, both directly and indirectly, through energetic arousal as a mediator. Conclusions: The results showed a relationship between affective temperaments and insomnia symptoms and included the role of energetic arousal, a mood state dimension, as a mediator.