Objective To determine the risk of non-fatal self harm in the 12 months after discharge from psychiatric inpatient care. Design Cohort study based on national hospital episode statistics. Setting England. Population Patients aged 16-64 years discharged from psychiatric inpatient care between 1 April 2004 and 31 March 2005 and followed up for one year. Results 75 401 people were discharged from psychiatric inpatient care over the study period, 4935 (6.5%) of whom were admitted at least once for self harm in the following 12 months. Risk of self harm was greatest in the four weeks after discharge; one third (32%, n=1578) of admissions for self harm occurred in this period. The strongest risk factor for self harm after discharge was admission for self harm in the previous 12 months (hazard ratio 4.9, 95% confidence interval 4.6 to 5.2). The risk of self harm was also higher in females, younger people, those with diagnoses of depression, personality disorders, and substance misuse, and those with short lengths of stay. Conclusion More than 6% of patients discharged from psychiatric inpatient care are readmitted for an episode of self harm within 12 months, with one third of these episodes occurring in the month after discharge. Self harm after discharge from hospital shares many of the features of suicide after discharge. Interventions should be developed to reduce risk in this period.