Adrenocortical carcinomas are rare tumors. In the absence of the gold standard that constitutes metastases, local invasion or recurrence, the diagnosis of malignancy may represent a great challenge for both clinicians and pathologists. Several multiparametric systems have been developed to assess this malignancy. Among them, the Weiss system, established in 1984 and based on nine microscopic criteria, appears to be the most employed because of its simplicity and reliability. The presence of three and more criteria is in favor of malignancy. However, the application of such system is not devoid of difficulties and subjectivity. A more precise definition of the different microscopic criteria and the proposition of a modified Weiss system based on the most reliable criteria could help. Besides, the Weiss system is of limited value for the diagnosis of malignancy in oxyphil tumors and children tumors of the adrenal cortex.