PURPOSE:The purpose of the study was to examine the long-term influence of involuntary hospitalization on medication adherence, engagement in out-patient treatment and perceived coercion to treatment participation. METHODS:In a naturalistic observational multi-centre study, 290 voluntarily and 84 involuntarily hospitalized patients with schizophrenia or schizoaffective disorder had been followed up over a period of 2 years with half-yearly assessments. Assessments included self-rated medication adherence, externally judged medication adherence by blood levels, engagement in treatment and perceived coercion. The statistical analyses were based on multilevel hierarchical modelling of longitudinal data. Level and development of the outcome was controlled for involuntariness, for sociodemographic characteristics and clinical history. RESULTS:Involuntariness of the index-hospitalization did not have an effect on the development of treatment engagement or medication adherence judged by blood levels in the course of the follow-up period when the models were controlled for sociodemographic variables and clinical history. It was associated, though, with a continuously lower self-rated medication adherence. Moreover, former involuntarily hospitalized patients more often felt coerced in several treatment aspects at the follow-up assessments. Yet, there was no difference between the voluntary and involuntary group with regard to the development of the levels of adherence or coercion experiences over time. CONCLUSIONS:Involuntary hospitalization does not seem to impair future treatment engagement in patients with schizophrenia, but formerly involuntarily hospitalized patients continue to be more sensitive to subjective or real coercion in their treatment and more vulnerable to medication non-adherence. Hereby, their risk of future involuntary hospitalization might be increased.