Flat epithelial atypia is a descriptive term that encompasses lesions of the breast terminal duct lobular units in which variably dilated acini are lined by one to several layers of epithelial cells, which are usually columnar in shape and which display low-grade cytologic atypia. Observational studies have suggested that at least some of these lesions may represent either a precursor of ductal carcinoma in situ (DCIS) or the earliest morphological manifestation of DCIS. In contrast, the limited available clinical follow-up data suggest that the risk of both local recurrence and progression of these lesions to invasive cancer is extremely low, supporting the notion that categorizing such lesions as 'clinging carcinoma' and managing them as if they were fully developed DCIS will result in overtreatment of many patients. Additional studies are needed to better understand the biological nature and clinical significance of these lesions.