Abstract Introduction: The importance of breast cancer patients (BPs) being supplied with sufficient information is well known. This study investigated the unfulfilled psychosocial information requirements of multimorbid BPs. Methods: This study records the unfulfilled psychosocial information requirements of 4166 patients, who were treated at one of the fifty breast centres in North Rhine Westphalia. The Cologne patient questionnaire for breast cancer 2.0 included in the postal survey following hospital stays records the information requirements using an adapted version of the “Cancer patient information needs” scale. Through a univariate analysis using the χ 2 test, it was investigated whether multimorbid BPs had significantly different psychosocial information requirements than BPs without further concomitant illnesses. Results: In general, it transpired that BPs had relatively low unfulfilled information requirements regarding work (20.7 %), everyday life (26.8 %), illness (27.4 %) and treatment (35.7 %), though such requirements were higher when it came to health-related behaviour (54.2 %). Multimorbid BPs had significantly lower unfulfilled information requirements regarding work and significantly larger ones regarding treatment in comparison to BPs without concomitant illnesses. Renal diseases and concomitant mental illnesses were associated with particularly high information requirements (p < 0.05). Conclusion: The results of our study should clarify the complexity and heterogeneity of information requirements of breast cancer patients in oncological care and should help to design the supply of information to be more patient-oriented.