The aim of this analysis was to evaluate adherence of postmenopausal patients with early invasive hormone-dependent breast cancer to treatment with adjuvant non-steroidal aromatase inhibitors, vitamin D and calcium (if they were prescribed by their oncologists) in every day clinical practice in Croatia. The aim of this analysis was also to evaluate adherence of Croatian oncologists to the bone health guidelines and to the follow-up criteria as suggested by the current national and international guidelines for women with breast cancer receiving adjuvant endocrine therapy. In this prospective, noninterventional study a total of 438 postmenopausal patients receiving adjuvant endocrine treatment with non-steroidal aromatase inhibitors anastrozol or letrozol were included. Patients were followed up for an average 23.5± 4.9 months. Average number of oncological visits was 5.3. Patients who took ≥80% of the prescribed dose were considered adherent. In our study self-reported adherence to aromatase inhibitors was 97% (425/438 patients) and there were only 13 (3%) non-adherent patients. Vitamin D and calcium were prescribed to only 329/438 (75.1%) patients at some point during the study. Self-reported adherence to vitamin D and calcium was 88.4%, and there were 38/329 (11.6%) non-adherent patients. Osteoporosis was diagnosed in 24 patients (5.5%) of the total study population, bearing in mind that 258/438 (59%) patients did not have densitometry. Bisphosphonates were prescribed to 54/438 (12.3%) patients, whilst only 19 (35.2%) of those had osteoporosis. On the other hand, there were still patients with osteoporosis who were not treated with bisphosphonates. These results shows that in significant number of our patients (36.5%) bone health was compromised because of lack of oncologists' adherence to the bone health guidelines (24.9% of patients did not have vitamin D and calcium prescription) and because of patientsʼ non-adherence to vitamin D and calcium (11.6%). Densitometry was performed in only 180/438 patients (41.1%) and this data also shows as above, bad compliance to the bone health guidelines by oncologists. Compromised bone health is often associated with deteriorated patients' quality of life, and increased medical costs what is important issue in already overstretch health care budgets in transitional countries. Our analysis among postmenopausal women with breast cancer receiving adjuvant endocrine therapy also shows that more unnecessary and unproven follow-up procedures (chest radiograph, abdominal ultrasound, tumor markers CEA and CA 15-3) were done compared to the guidelines’ recommendations. The use of diagnostic tests not proven to increase survival during standard follow-up of early breast cancer patients, is not cost-effective and has become a large, unnecessary burden for overstretched and limited transitional countriesʼ budgets. Improved adherence to the current guidelines can substantially cut medical costs, reduce risks and improve patient quality of life without adversely affecting outcome.