Studies on the frequency and the overall trend in recent years of aggressive assaults by patients in German psychiatric hospitals are scarce. We investigated the frequency of physical aggression by patients between 2008 and 2015 in two hospitals for psychiatry and psychotherapy. Aggressive and violent events were routinely assessed (spontaneous reports) and were analyzed in a differentiated way. The frequency of aggressive behavior of patients towards others showed a slightly, but significantly increase since 2008, although at a low level. This increase was almost entirely caused by an increase of aggressive assaults against nursing staff. The relative frequency of aggressive behavior by patients (4/1000 cases) was on average rather low. The increase of assaults particularly against nursing personnel gives nonetheless reason to scrutinize and continuously optimize measures for prevention and therapy of patients' aggressive behavior.