Congenital sinuses or fistulas of the lip are uncommon malformations, yet true medial upper-lip fistulas (MULFs) are extremely rare. We present a new case of congenital upper-lip fistula located in the midline of the philtrum of an 8-month-old girl. Complete surgical removal was performed with a combined extra- and intraoral approach. Histological examination revealed that the fistula was lined by squamous epithelium with sebaceous and mucous glands and hair follicles. Several embryological hypotheses have been proposed concerning these anomalies. This article reexamines and discusses major embryological theories on pathogenesis of sinuses or fistulas of the upper lip. We propose that early ectodermal inclusion events may occur in the medial fusion area during formation of the intermaxillary process. This embryological approach is highly concordant with our recent hypothesis on nasal dermoid sinus cysts (NDSCs) pathogenesis, in which we proposed an embryological hypothesis with early ectodermal inclusion phenomenon in the midline suture area to explain NDSCs pathogenesis. Common early ectodermal inclusion phenomena could be involved in both NDSCs and MULFs pathogenesis.