Scrotal abscess in infancy is rare and, in an otherwise healthy infant, an unexpected pathology. We present a 2-week-old boy with a unilateral scrotal swelling, imaged by high-resolution sonography. Sonography with colour Doppler demonstrated an encapsulated heterogeneous mass in the left scrotum with surrounding hyperaemia and a hypervascular spermatic cord. The testis was not demonstrable with full certainty and surgical exploration was undertaken. A scrotal abscess, indistinguishable from the testis and epididymis, had to be resected and on histology was found to have originated from the tunica vaginalis. Urogenital investigations did not reveal any associated abnormality and the final diagnosis was idiopathic scrotal abscess. High-resolution sonographic features with colour Doppler of a scrotal swelling can suggest an abscess and help determine appropriate therapy.