Objective: To explore the potential ADHD phenotype of ADHD-without reported insomnia in comparison with controls and their tolerance of stimulants in a cohort rigorously screened for comorbidities. Method: Adults meeting Diagnostic and Statistical Manual of Mental Disorders (4th ed., text rev.; DSM-IV-TR) criteria for ADHD-without insomnia and matched controls were administered a sleep/medication-timing questionnaire and the Pittsburgh Sleep Quality Index. Results: Among 105 participants, ADHD participants scored in the mild insomnia range and showed reduced sleep quality compared with controls, F(3, 101) = 34.9, p <.05, but no delay in bedtime/mid-sleep-time circadian measures. Sleep quality was similar between stimulant, nonstimulant, and unmedicated groups, χ22 = 0.445, p =.80. However, later timing of stimulant dosing was correlated with later sleep times, p <.01. Conclusion: We isolated a potential phenotype of ADHD-without circadian delay in adults who demonstrated insomnia/sleep quality disturbance by sleep instrument, but lacked sleep-timing delay. Nevertheless, sleep delays were associated temporally with late-dosed stimulants in this group. © 2012 SAGE Publications.