ABSTRACT Objective: Differentiate the atypical angiomyolipoma from the renal cell carcinoma of the same size by computed tomographic findings. Introduction: A solid renal mass is a lesion without macroscopic fat that enhances regardless of its pattern. It is important to detect the malignant one and differentiate them from the benign one, especially when they are small. To maximize its detection and characterization, CT includes images obtained before and after the administration of intravenous contrast. Materials and methods: A prospective study was carried out with 45 patients (7) with atypical angiomyolipomas and (38) with renal cell carcinoma, all cases had been nephrectomized (total or partial) for the resection of the lesion with subsequent evaluation of it in the pathology center, using three-phase computed tomography (phases without contrast, corticomedullary and early excretory) for renal cell carcinoma less than 50 mm. Two expert radiologists individually evaluate the characteristics of the tumor, its attenuation in phase without contrast and the characteristics of its enhancement to differentiate the atypical angiomyolipoma from renal cell carcinoma Results: There was a predominance of women with atypical AML (57.1% of the total; n = 4) and of men with RCC (65.15%; n = 25), but no significant difference seen between them. Significant difference is seen between atypical AML and RCC regarding their contour (p-value = 0.043). In the post-contrast phase, atypical AMLs had a homogeneous distribution enhancement in 6 cases (85.7%) and a prolonged enhancement pattern over time in most of cases (71.4%, n= 5); regarding the RCCs presented heterogeneity in most of cases (92.1%, n= 35) and early wash out enhancement pattern in (81.6%, n= 31), with significant difference between them. Conclusion: Three-phase helical CT is the standard modality for evaluate the SRM less than 50 mm. It serves to differentiate the Atypical AML from the RCC, with the more valuable tomographic findings are homogeneity and pattern of enhancement of renal mass.