BackgroundInequality in health and treatment of disease across socioeconomic status groups is a major public health issue.AimsTo examine differences in socioeconomic status in common mental disorders and use of psychotherapy provided by the public and private sector in the UK between 1991 and 2009.MethodDuring these years, 28 054 men and women responded to annual surveys by the nationally representative, population-based British Household Panel Survey (on average 7 measurements per participant; 207 545 person-observations). In each year, common mental disorders were assessed with the self-reported 12-item General Health Questionnaire and socioeconomic status was assessed on the basis of household income, occupational status and education.ResultsHigher socioeconomic status was associated with lower odds of common mental disorder (highest v. lowest household income quintile odds ratio (OR) 0.88, 95% CI 0.82–0.94) and of being treated by publicly provided psychotherapy (OR = 0.43, 95% CI 0.34–0.55), but higher odds of being a client of private psychotherapy (OR = 3.33, 95% CI 2.36–4.71). The status difference in publicly provided psychotherapy treatment was more pronounced at the end of follow-up (OR = 0.36, 95% CI 0.23–0.56, in 2005–2009) than at the beginning of the follow-up period (OR =0.96, 95% CI 0.66–1.39, in 1991–1994; time interaction P<0.001). The findings for occupational status and education were similar to those for household income.ConclusionsThe use of publicly provided psychotherapy has improved between 1991 and 2009 among those with low socioeconomic status, although social inequalities in common mental disorders remain.