Background: Mixed anxiety and depressive disorder (MADD) is common yet ill-defined, with little known about outcomes. Aims: To determine MADD outcomes over 1 year. Method: We recruited 250 adults attending seven London general practices with mild moderate distress. Three groups were defined using a diagnostic interview: MADD, other ICD-10 psychiatric diagnosis, no psychiatric diagnosis. We assessed symptoms of distress (General Health Questionnaire-28), quality of life (12-item Short Form Health Survey), general practitioner (GP) diagnosis and consultation rate at baseline, 3 months and 1 year. Results Two-thirds of participants with MADD had no significant psychological distress at 3 months (61%) or 1 year (69%). However, compared with those with no diagnosis, individuals had twice the risk of significant distress (incidence rate ratio 2.39, 95% CI 1.29-4.42) at 3 months but not 1 year, and persistently lower quality of life (mental health functioning). There was no significant difference in GP consultation rate/diagnosis. Conclusions: The majority with MADD improved, but individuals had an increased risk of significant distress at 3 months and a lower quality of life. As we cannot currently predict those with a poorer prognosis these patients should be actively monitored in primary care.