OBJECTIVE: To investigate the incidence and severity of adverse drug reactions of cyclosporine using AUC-targeted therapeutic drug monitoring (TDM) compared to trough level (Ctrough )-targeted TDM in adult allogeneic stem cell recipients. METHODS: Blind, monocenter, intervention study. Subjects were 1:1 randomized into either an AUC group or a Ctrough group. Adverse drug reactions were accessed two and four weeks after start of treatment. RESULTS: Forty patients were included, resulting in 15 evaluable subjects (AUC group) and 13 evaluable subjects (Ctrough group). Grade two/three toxicity was observed in 46% (Ctrough group) versus 60% of subjects (AUC group) (P = .463). There was no significant difference between two and four weeks after start of cyclosporine for nausea (P = .142 resp. P = .122), renal dysfunction (P = .464 resp. P = 1.000), and hypomagnesemia (P = 1.000 resp. P = .411). Subjects in the AUC group reached the therapeutic goal earlier (72,7% versus 43,0% at third sampling point, P = .332) and were within the target range more consistently. CONCLUSION: This study showed no reduction in incidence and severity of cyclosporine-induced toxicity with AUC- versus trough level-targeted TDM. Although modeled dosing based on AUC led to faster optimal target attainment, this did not result in less toxicity in the early days after transplantation