BACKGROUND: Approximately 20% of children with attention-deficit hyperactivity disorder (ADHD) experience clinical levels of impairment into adulthood. In the UK, there is a sharp reduction in ADHD drug prescribing over the period of transition from child to adult services, which is higher than expected given estimates of ADHD persistence, and may be linked to difficulties in accessing adult services. Little is currently known about geographical variations in prescribing and how this may relate to service access. AIMS: To analyse geographic variations in primary care prescribing of ADHD medications over the transition period (age 16-19 years) and adult mental health service (AMHS) referrals, and illustrate their relationship with UK adult ADHD service locations. METHOD: Using a Clinical Practice Research Datalink cohort of people with an ADHD diagnosis aged 10-20 in 2005 (study period 2005-2013; n = 9390, 99% diagnosed <18 years), regional data on ADHD prescribing over the transition period and AMHS referrals, were mapped against adult ADHD services identified in a linked mapping study. RESULTS: Differences were found by region in the mean age at cessation of ADHD prescribing, range 15.8-17.4 years (P<0.001), as well as in referral rates to AMHSs, range 4-21% (P<0.001). There was no obvious relationship between service provision and prescribing variation. CONCLUSIONS: Clear regional differences were found in primary care prescribing over the transition period and in referrals to AMHSs. Taken together with service mapping, this suggests inequitable provision and is important information for those who commission and deliver services for adults with ADHD.