['To evaluate the effects of a collaborative pharmacy benefits manager (PBM)/ health plan-administered drug therapy management (DTM) program on healthcare utilization and costs in patients with diabetes treated with polypharmacy.', 'Retrospective quasi-experimental design with comparison group.', 'This DTM program was a collaborative effort between the PBM, PerformRx, and the care management departments of Keystone First (KF) and AmeriHealth Caritas Pennsylvania (ACP) care management departments, targeting patients with diabetes using >15 medications. Pharmacists reviewed member profiles and made evidencebased prescriber and patient interventions, working directly with prescribers and indirectly with members, via care managers. Care managers provided additional services not otherwise within the scope of DTM. The study group consisted of 954 DTM participants reviewed by a pharmacist between November 1, 2010, and July 31, 2011. The control group consisted of 810 matched DTM participants not reviewed by a pharmacist.', 'Intervention acceptance rates for KF and ACP were 33% and 26%, respectively. The study group demonstrated lower inpatient admissions and emergency department utilization rates, although only the KF study group inpatient admission rate achieved statistical significance (76.4%; P = .0002). The study groups realized statistically significant total cost savings (pharmacy + medical) compared with their corresponding control groups (47.8% KF, P = .0039; 50.7% ACP, P = .0497) despite non-statistically significant increases in pharmacy costs.'] Does collaborative DTM reduce hospitalization and healthcare costs in patients with diabetes treated with polypharmacy?