Background and purpose: Bipolar disorder is a mood disorder and mental illness that is recognized as type I and type II. Bipolar I disorder involves at least one episode of mania and is a common chronic recurrence disease with various causes responsible for its recurrence. The aim of this study was to determine effective factors on relapsing disease in patients with bipolar I disorder using frailty model.

Materials and methods: The information of 268 patients with bipolar I disorder who were hospitalized in Farshchian Hospital, Hamedan, Iran (2008-2014) were collected using their records. Patients hospitalized due to more than one recurrence were entered the study. The intervals between recurrence times were recorded. FrailtyPack of R software was used to fit model. 

Results: The mean age of patients was 34.10±11.56 years, and 160 patients (72.7%) were male. In total, 696 recurrences occurred in 268 patients. The number of recurrences was between 2 to 7 times. All patients experienced at least 2 recurrence episodes. The results of fragmented frailty model practice showed significant effect of age, race, place of residence, crime, and type of treatment on relapsing time (P<0.05).

Conclusion: Many factors, including demographics and illness characteristics might cause the recurrence of bipolar disorder, therefore identifying these factors can help in preventing or reducing the incidence of recurrence of this disease.