Analysis of the General Practice Research Database by former Regional Health Authority (RHA) areas for 1994 shows that there was relatively little geographical variation in prevalence of treated asthma. All regions are within 15% of the value for England & Wales. Age-standardised prevalence rates varied from 5.9% (SW Thames) to 7.1% (Mersey and East Anglian) for males and from 5.7% (NW Thames) to 7.4% (Mersey) for females.