Background This study aimed to evaluate physical fitness and body composition in a sample including hospitalized patients with bipolar disorder and to compare them with a population‐based sample. Methods In this comparative observational study, 40 bipolar patients and 40 healthy subjects in Taleghani Hospital, Tehran, Iran, in 2019 were assessed. The physical fitness items such as body mass index (BMI), body fat, push‐up test, curl‐up test, VO2 peak, and sit and reach test were compared across the groups. Young Mania Rating Scale for assessing the severity of bipolar disease and WHODAS2.0 for the estimation of global performance were done in the case group. Results The results of this study demonstrate that sit and reach test, body mass index (BMI), and body fat percent were similar across the studied groups. The push‐up test, curl‐up test, and VO2 peak (P = .001) were significantly lower in the case group. In the case group, only the push‐up test was associated with the severity of bipolar disorder and decreased performance. Conclusion Lower push‐up and curl‐up can indicate an increase in both back and neck pains in these patients. Low VO2 peak in these patients increases the risk of heart disease and mortality rates in bipolar patients. The push‐up test can be used as a screen test to estimate the severity of the bipolar disorder.