Objective: The authors explored associations between ADHD symptoms, seasonal depressive symptoms, lifestyle, and health. Method: Adult ADHD patients ("n" = 202) and controls ("n" = 189) completed the ASESA questionnaire involving lifestyle, eating pattern, and physical and psychological health, and validated measures on ADHD and sleep. ASESA is the Dutch acronym for Inattention, Sleep, Eating pattern, Mood, and General health questionnaire. Results: Indication for delayed sleep phase syndrome (DSPS) was 26% in patients and 2% in controls (p less than 0.001). Patients reported shorter sleep, longer sleep-onset latency, and later midsleep. Shorter ("R"[superscript 2] = 0.21) and later ("R"[superscript 2] = 0.27) sleep were associated with hyperactivity, male gender, younger age, and seasonal depressive symptoms. Seasonal depressive symptoms were related to hyperactivity, female gender, unemployment, and late sleep (pseudo "R"[superscript 2] = 0.28). Higher body mass index (BMI) was associated with shorter sleep in patients (rho = -0.16; "p" = 0.04) and controls (rho = -0.17; "p" = 0.02). Longer sleep showed lower odds for indication of metabolic syndrome (OR = -0.17; "p" = 0.053). Conclusion: DSPS is more prevalent in ADHD and needs further investigation to establish treatment to prevent chronic health issues. (Contains 5 tables.)