Objective: To examine current immunosuppressive regimens administered to kidney transplant recipients (KTRs) in South-eastern Europe. Methods: This was a 12-month, multicenter, non- interventional, prospective, observational study of immunosuppressive regimens in adult de novo and maintenance KTRs. The primary endpoint was to identify the number, type, dosage and trough concentrations (C0) of immunosuppressive medications. Results: Data were available for 1774 KTRs from five countries (Bulgaria [n = 109], Croatia [n = 339], Romania [n = 647], Serbia [n = 434] and Slovenia [n = 245]). The most common immunosuppressive regimen in all countries was a triple therapy regimen (de novo KTRs, 67.9 – 100% at baseline and 67.3 – 100% at end of study ; maintenance KTRs, 48.8 – 90.7% and 43.2 – 90.1%, respectively). The most frequent regimen in de novo KTRs comprised tacrolimus, mycophenolate mofetil (MMF) or mycophenolate sodium (MPS), and corticosteroids. In maintenance KTRs, the most frequent regimen was tacrolimus or cyclosporine, and MMF or MPS, with or without corticosteroids. A C0 of <5 ng/mL was recorded in 40.2% of immediate-release and 48.7% of prolonged-release tacrolimus patients ; 79.5% of patients taking cyclosporine had a C0 of <75 ng/mL. Infections were the most common adverse event (358/597, 60.0%), mainly urinary tract infections (208/358, 58.1%). Conclusions: Triple therapy—comprising a calcineurin inhibitor (CNI ; tacrolimus or cyclosporine), antiproliferative drugs (MMF or MPS) and corticosteroids—was the most common immunosuppressive regimen used in KTRs in South- eastern Europe. Individual CNI C0 were below the target range in a substantial proportion of KTRs, highlighting the need to maintain therapeutic drug monitoring of immunosuppressive therapy in this patient population.