Background: Although a number of effective treatments are available for patients on inpatient psychiatric units, the motivation of patients to engage with these treatments is frequently poor. Unmotivated patients may be more likely to drop out of treatment, or discontinue treatment after discharge. Aim: The present study examined the relationship of depression and ward atmosphere in influencing motivation. Methods: Using a cross-sectional design, 60 patients at a South London Medium Secure Unit completed the Centre for Epidemiological Studies Depression Scale, the Ward Atmosphere Scales and the Patient Motivation Inventory. Results: Regression analyses demonstrated that depression predicts motivation in a relationship that is mediated by ward atmosphere. In addition, ward atmosphere predicts motivation in a relationship that is mediated by depression. Conclusions: The findings suggest a reciprocal relationship between depression and ward atmosphere, and both factors are important in influencing a patient's motivation to engage with treatment. Improving motivation of psychiatric inpatients seems to require both factors to be addressed.