The purpose of this study was to determine the ultrasonographic (US) appearance of focal Hashimoto's thyroiditis (FHT). Thirty-seven FHT patients and 60 consecutive patients with 60 papillary thyroid carcinomas (PTC) that were confirmed by cytology or histopathology between January 2011 and December 2013 were analyzed. Using the results of color Doppler imaging, US findings were retrospectively reviewed. Inter-group differences in size, internal content, echogenicity, echo texture, shape, boundary, margin, calcifications, fine echogenic septa, and blood flow were statistically assessed. The US appearances of the FHTs examined were: solid (100%), hypoechoic (97%), heterogeneous (68%), ovoid-to-round shape (73%), well-defined boundary (95%), smooth margin (89%), and hypervascular (46%). Ovoid-to-round shape, well-defined boundary, fine echogenic septa, and hypervascularity were significantly more prevalent for FHTs than for PTCs (p < 0.05). Ovoid-to-round shape and fine echogenic septa have a higher specificity and positive predictive value. FHTs show a spectrum of US appearances, making FHT diagnosis cumbersome. Fine echogenic septa are highly specific for FHT. Ovoid-to-round shape, well-defined boundary and hypervascularity may possibly be associated with FHT.