Most of the adrenal tumors that are incidentally detected are benign adenomas. The incidence of malignant adrenal tumors including adrenocortical carcinoma (ACC) and primary adrenal lymphoma (PAL) is rather low. As many patients with ACC and PAL are diagnosed at an advanced stage of disease, the overall survival time of both entities remains poor. The therapeutic strategies for both entities differ. Thus an early differentiation between ACC and PAL is necessary. Unfortunately hitherto preoperative diagnosis of potentially malignant adrenal masses is still a main problem in the treatment of adrenal tumors. We present the case of a 57-year-old male patient with ACC and the case of an 87-year-old male patient with PAL and provide a systematic comparison of the clinical and pathological features of both entities. In both cases clinical and radiological features resulted in an initially false diagnosis. Primary surgical therapy was performed in both patients. The patient with PAL died five months after initial surgery. The patient with ACC showed tumor progression with local and systemic recurrence despite adjuvant therapy with mitotane and additional surgical therapy. Prognosis of patients with ACC and PAL seems to be dependant on the ability to start accurate treatment without any time delay. We propose some guidelines for diagnosis and surgical management of adrenal tumors.