Background <p>Adrenocortical carcinoma (ACC) is a rare and aggressive malignancy in which cortisol secretion has been associated with poor survival. However, whether this adverse prognosis reflects intrinsically more aggressive tumor biology or merely established pathological predictors remains uncertain.</p> Methods <p>We conducted a single-center retrospective cohort of adults with histologically confirmed ACC. Tumors were classified by functional status. Aggressive pathology (Ki-67 ≥ 20%, mitotic rate ≥ 20/50 HPF, or R1/R2 margins) was compared across subgroups, and survival was analyzed using Kaplan–Meier methods.</p> Results <p>Thirty-nine patients were included. Cortisol-secreting tumors exhibited higher Ki-67 and mitotic rates, a greater frequency of incomplete resection, and higher use of adjuvant mitotane compared with non-functioning and androgen-secreting ACC. These differences persisted when analyses were restricted to advanced ENSAT stage (III–IV). Cortisol secretion was strongly associated with fulfillment of the composite aggressive pathology endpoint and identified discordant cases with low ENSAT stage but adverse pathological features. Increasing pathological aggressiveness across functional subgroups was confirmed by trend analyses. Overall survival differed by functional status, with the worst outcomes in cortisol-secreting ACC, even after adjustment for age and sex. Importantly, cortisol secretion further stratified prognosis among tumors with Ki-67 ≥ 20%, indicating adverse prognostic information beyond proliferative activity alone.</p> Conclusions <p>Cortisol-secreting ACC is associated with a distinct and more aggressive pathological and clinical phenotype. Hormonal functional status provides prognostic information beyond ENSAT stage and proliferative indices, supporting its integration into contemporary risk stratification frameworks.</p>