Objective: Our objective was to evaluate the long-term impact of n-of-1 trials-within-patient randomised, double-blind, cross-over comparisons of stimulant versus placebo or stimulant-on ADHD management. Methods: Telephone surveys at 3, 6 and 12 months. Main outcome measures included (1) changes in treatment before and after the n-of-1 trial, (2) congruence of management at follow-up with trial result, (3) reasons for any non-congruence, and (4) persistence of the joint patient-doctor decision over 12 months. Patients were children with clinically diagnosed ADHD, aged 5-16 years. Results: A total of 76 patients were followed up; 12 months' data were available for 67 (88%). Management changed from baseline for 46, 48 and 51% at 3, 6 and 12 months respectively. Most responders, 21/37 (57%), remained on the same stimulant at 12 months, compared to 9/24 (37%) non-responders. Of the remaining non-responders, 15/24 (62%) either switched (2/24, 8%) or ceased stimulants (13/24, 54%). The rate of congruence with the test result was 45/65 (69%) at 3 months, 44/67 (66%) at 6 months and 40/67 (60%) at 12 months. Persistence with the post-trial decision over 12 months was high (79-85%) whether the decision was to continue or to cease stimulants. Conclusions: Although not conclusive because there was no control group, our results suggest that n-of-1 trials may improve rational treatment of ADHD.