OBJECTIVES: Diagnosis of children with attention-deficit/hyperactivity disorder (ADHD) is increasing. Recent studies have shown a tendency for younger children in a school cohort being diagnosed with the condition, suggesting the diagnosis is associated with immaturity. Given potential sequelae of treatment, there is a great need to evaluate potential misdiagnosis.  The present study sought to identify characteristics and treatment patterns of children with ADHD, compare younger to older children within single age cohorts, and find seasonality and trends in disparity of diagnosis and pharmacotherapy, within a non-selective real-world setting.   METHODS: Children aged 6-11 who were members of Clalit Health Services January 2010. Diagnosis (ICD-9 314.[0,1,2,8,9]) and medication (ATC codes 'N06BAx') were extracted from the Clalit Health Services database. Calendar months of first diagnosis (2003-2011) and months of drug purchases (2010-2011) were compared by month of birth. Trends of diagnosis and treatment were determined for the various sub-cohorts, and population sector differences were compared. RESULTS: Of total population (400,828 children, 51% male), 40467 (10.1%) were diagnosed with ADHD and 33188 (8.3%) were treated (usually methylphenidate). Diagnosis levels for younger (Y: Aug-Nov) children (10.9%) were lower than older (O: Dec, Jan-March) children (9.2%, RR 1.18 CI 1.16 to 1.21). The rate disparity was higher beginning school-year (September-December; RR 1.21 CI 1.17-1.26). Any-purchase dispensing RR was 1.19 (CI 1.16 to 1.22), while monthly RR was 1.18 (1.17-1.19). RR for dispensing was stable between age-cohorts (1.17-1.22) without trend. Among children purchasing drugs, the seasonal variation in drug purchases (adherence) is similar Y:O CONCLUSIONS: ADHD diagnosis and medication are common in the primary school population. The increased incidence and prevalence among younger children in a cohort questions the appropriateness of both diagnosis and medication, suggesting behavioral treatment may often be more suitable to avoid long term costs and deleterious effects, than pharmacological intervention.