Studies of urban-rural differences in prevalence of non-psychotic mental disorder have not given consistent findings. Such differences have received relatively little study in Great Britain. Data from 9777 subjects in the Household Survey of the National Morbidity Survey of Great Britain were analysed for differences between urban, semi-rural, and rural areas. Psychiatric morbidity was assessed by scores on the Revised Clinical Interview Schedule (CIS-R), together with alcohol dependence, drug dependence, and receipt of treatment from general practitioners. Associations with other characteristics were examined by logistic regression. Urban subjects had higher rates than rural of CIS-R morbidity, alcohol dependence, and drug dependence, with semi-rural subjects intermediate. Urban subjects also tended to be members of more deprived social groups, with more adverse living circumstances and greater life stress--factors themselves associated with disorder. Urban-rural differences in alcohol and drug dependence were no longer significant after adjustment for these factors by logistic regression, and differences on CIS-R morbidity were considerably reduced. There were no differences in treatment. There are considerable British urban-rural differences in mental health, which may largely be attributable to more adverse urban social environments.