Minor psychiatric morbidity is known to be associated with social disadvantage, but few studies have explored this association at the population level. This study reports data from a postal survey across 19 health districts in one region, with a total sample of 38,000 respondents. The percentage scoring above the General Health Questionnaire (GHQ) threshold for each health district was correlated with measures of deprivation derived from the 1991 census and standardised mortality ratios. Highly significant correlations were seen between the percentage above the GHQ threshold and the Underprivileged Area (UPA) score (r = 0.84), under 65 Standardised Mortality Ratio (SMR; r = 0.80), lack of amenities (r = 0.56), overcrowding (r = 0.54), lone-parent families (r = 0.84), unemployment (r = 0.87), unskilled workers (r = 0.77), ethnic minority composition (r = 0.58) and social mobility (r = 0.85). However, the three most deprived districts had the lowest response rates and when these were excluded from the analysis, only the correlations with under 65 SMR (r = 0.57, P < 0.05), UPA score (r = 0.52, P < 0.05) and unskilled workers (r = 0.60, P < 0.05) remained significant. There may be a threshold effect for the impact of social disadvantage on mental health, with much higher rates of psychological morbidity among markedly disadvantaged populations.