Inattention is a core symptom of attention deficit hyperactivity disorder (ADHD) and one of the main impairments resulting from insomnia disorders. These disorders have also been reported to be linked with disturbances in circadian rhythms and with increased eveningness. To explore these associations, more than 550 adults were surveyed across Romania. Using self-reported questionnaires, the presence and severity of ADHD and insomnia symptoms were determined, together with sleep and circadian typology parameters. ADHD symptoms were more frequent and severe among younger individuals. Subjects with probable ADHD complained more frequently of sleep disturbance of the insomnia type (more than 50 %) and reported shorter sleep durations and longer sleep latencies and more frequent unwanted awakenings. Individuals likely to suffer from ADHD and/or insomnia disorder were significantly more evening oriented than controls. Inattention was associated with both insomnia and eveningness, while impulsivity was associated with poor sleep. Hyperactivity and sleep timing were associated with poor sleep only in probable insomnia group. These findings highlight the reciprocal links between ADHD symptoms, sleep and diurnal preference.