Background. Relatively little is known regarding stability or change over time in milder psychiatric disorder identified in epidemiological studies.

Methods. Data were analysed on 2890 subjects from the 1946 British birth cohort study. Psychiatric disorder was identified at age 36 years using the Present State Examination Index of Definition and 7 years later at age 43 using a symptom scale, employing a threshold to give identical 6% prevalence of disorder. Predictors were derived from recent social data and information collected earlier in childhood and younger adulthood.

Results. Over 7 years, there was considerable movement between case and non-case status. Only 1·7% of the sample satisfied case criteria at both points. Approximately two-thirds of cases at age 36 had fallen below case levels at age 43 and two-thirds of cases at age 43 were new cases. Most onsets and remissions were between definite case and non-case levels, rather than around the threshold. The strongest predictors of onset and remission were recent demographic, social and life stress variables, and earlier reported nervous disorder, with contributions from parental social background, and life history variables in adolescence.

Conclusions. There is considerable change over 7 years in milder psychiatric disorder, with around two-thirds of it episodic or fluctuating and one-third chronic. Recent social variables are strong predictors of change or chronicity, with some lasting contributions from childhood social setting and earlier life history.