To assess adherence to the current European Society for Medical Oncology (ESMO) clinical practice guideline on bone health in cancer patients and the German guidelines for lung, breast, and prostate cancer among German oncologists in hospitals and office-based physicians and to identify predictors of guideline compliance to assess the needs for dedicated training.This was a retrospective sample analysis representing hospitals and office-based physicians in Germany in 2016. Records from lung, breast, and prostate cancer patients who had received a diagnosis of bone metastasis between April 1, 2015, and March 31, 2016, were included. Oncologists at participating centers answered a self-assessment survey on aspects related to their professional life, including guideline adherence and years of clinical experience in medical oncology. Guideline adherence rates were assessed from patient records. Treatment variables and survey data were used to identify predictors of guideline compliance in a Classification and Regression Tree (CART) analysis.Disregarding recommendations for supplementation of calcium and vitamin D, guideline adherence among physicians treating lung, breast, or prostate cancer patients was 62%, 92%, and 83%, respectively. Compliance was 15%, 42%, and 40% if recommendations for dietary supplements were taken into account. Identified predictors of guideline compliance included treatment setting, medical specialty, years of professional experience, and frequency of quality circle attendance.Compliance with the ESMO and the German guidelines in cancer patients varies between medical specialties. In particular, patients with lung cancer and bone metastases often do not receive the recommended osteoprotective treatment and required supplementation. Discrepancies between guideline recommendations and common practice should be addressed with dedicated training.