Summary Objective LIN28 control cells reprogramming and pluripotency mainly through miRNA regulation and has been overexpressed in many advanced cancers. In this study, we evaluated the prognostic role of LIN28 and its regulatory miRNAs in a large cohort of adrenocortical tumours (ACTs). Patients and methods LIN28 protein expression was assessed in 266 adults ACTs (78 adenomas and 188 carcinomas) from Brazil and Germany. LIN28A and LIN28B gene expression was analysed in 59 ACTs (31 adenomas and 28 carcinomas) and copy number variation in 39 ACTs. In addition, we determined the expression of let‐7 family, mir‐9, mir‐30 and mir‐125 in 28 carcinomas. Results LIN28A gene was overexpressed in aggressive ACCs when compared with adenomas and nonaggressive ACCs, but no LIN28A copy number variation was found in ACTs. Unexpectedly, weak LIN28 protein expression was significantly associated with reduced disease‐free survival in ACC patients (P = 0·01), but for overall survival only a trend was detectable (P = 0·117). In the multivariate analysis, only Ki67 index ≥10% (HR 4·6, P = 0·000) and weak LIN28 protein expression (HR 2·0, P = 0·03) were independent predictors of recurrence in ACC patients. Interestingly, mir‐9 expression, a negative LIN28A/B regulator, was significantly higher in aggressive than in nonaggressive ACCs 2076 (from 36 to 9307) vs 133·4 (from 2·4 to 5193); P = 0·011 and was highly associated with reduced overall (P = 0·01) and disease‐free survival (P = 0·01). However, mir‐9 prognostic role should be further evaluated in a larger cohort. Conclusion Weak LIN28 protein expression was associated with recurrence in ACCs. Additionally, overexpression of mir‐9, a negative LIN28A regulator, was associated with poor outcome.