The pathologic evaluation of tumor nephrectomy specimens focuses on the diagnosis, grading, and staging of the neoplasm. The presence of coincidental non-neoplastic diseases in these specimens may have significant implications for patient outcomes. The purpose of this study is to determine the spectrum of non-neoplastic disease processes that may be overlooked in tumor nephrectomies, and to ascertain the extent to which surgical pathologists are trained to recognize these lesions. We reviewed the hematoxylin and eosin-stained slides of 246 adult tumor nephrectomy specimens with an emphasis on the non-neoplastic renal parenchyma. Further analysis of cases with pathologic alterations included special stains and direct immunofluorescence microscopy. The surgical pathology reports were reviewed to determine whether the non-neoplastic lesions were originally identified. We also surveyed United States pathology residency programs to determine how many require training in medical renal pathology. Forty-one cases (16.7%) had alterations, such as diffuse and/or nodular mesangial sclerosis, mesangial hypercellularity, or glomerular basement membrane thickening that warranted further study. After further work-up and clinical correlation, the pathologic changes in 24 cases were categorized as follows: diabetic nephropathy (19 cases) of which one demonstrated atheroembolic disease, thrombotic microangiopathy (3 cases), sickle cell nephropathy (1 case), and focal segmental glomerulosclerosis (1 case). Twenty-one (88%) of these diagnoses were not identified at initial pathologic evaluation. Only 35 of 98 pathology residency programs that responded to our survey require any formal training in medical renal pathology. Although accurate pathologic evaluation of renal neoplasms remains essential, surgical pathologists should be aware that coincidental non-neoplastic renal diseases are common, often not recognized, and may have important implications for patient care. Further consideration should be given to the training requirements of pathology residents and the guidelines for evaluation of nephrectomy specimens to avoid missing non-neoplastic renal lesions.