Introduction: ADHD is a common and growing problem which manifests and is diagnosed via a cluster of behaviours such as inability to regulate emotions or manage motivational delay and problems with executive functioning. It frequently accompanies autism spectrum disorders and dyslexia. Homoeopathy is a system of therapeutics based on the Law of Similars where 'like cures like'. Conditions are treated by highly diluted substances that cause, in healthy persons, symptoms like those of the condition to be treated. The aim of this case report is to describe the homoeopathic treatment and progress of one 16 year old youth with diagnoses of ADHD, Asperger's syndrome and dyslexia subjected to in-utero cannabis exposure. Methods: The youth received individualised homoeopathic medicines and additional ultra-molecular dilutions of cannabis. Outcome was measured using the parent completed Conner's Parent Rating Scale-Revised-Long version (CPRS:R-L) every 4 months, with DSMIV total score selected for analysis; and Measure Your Own Medical Outcome Measure (MYMOP) every 6 weeks, completed by parent and patient. Results: At start of treatment the patient's DSMIV total T score was 90+ (highest possible); after 18 months it was 59 (within normal range). MYMOP score at start of treatment was 4.5 and 1.75 after 18 months. Conclusion: Treatment by a homoeopath over 1 1/2 years was associated with improvements in ADHD status and patient generated outcomes. Ultra molecular dilutions of a recreational drug the patient was subjected to in-utero appear to have contributed to improvements. Systematic research with larger numbers would be required to confirm or refute this single case observation.