['Mitotane plasma concentrations ≥ 14 mg/l have been shown to predict tumor response and better survival in patients with advanced adrenocortical carcinoma (ACC). A correlation between mitotane concentrations and patient outcome has not been demonstrated in an adjuvant setting.', 'To compare recurrence-free survival (RFS) in patients who reached and maintained mitotane concentrations ≥ 1 4 mg/l vs patients who did not.', 'Retrospective analysis at six referral European centers.', 'Patients with ACC who were radically resected between 1995 and 2009 and were treated adjuvantly with mitotane targeting concentrations of 14-20 mg/l.', 'RFS (primary) and overall survival (secondary).', 'Of the 122 patients included, 63 patients (52%) reached and maintained during a median follow-up of 36 months the target mitotane concentrations (group 1) and 59 patients (48%) did not (group 2). ACC recurrence was observed in 22 patients of group 1 (35%) and 36 patients in group 2 (61%). In multivariable analysis, the maintenance of target mitotane concentrations was associated with a significantly prolonged RFS (hazard ratio (HR) of recurrence: 0.418, 0.22-0.79; P=0.007), while the risk of death was not significantly altered (HR: 0.59, 0.26-1.34; P=0.20). Grades 3-4 toxicity was observed in 11 patients (9%) and was managed with temporary mitotane discontinuation. None of the patients discontinued mitotane definitively for toxicity.'] Do mitotane levels predict the outcome of patients with adrenocortical carcinoma treated adjuvantly following radical resection?