Fibromatosis colli, also known as sternomastoid tumor, is considered a rare benign lesion of infancy of uncertain etiology and pathogenesis. Usually a self-limiting condition, diagnosis of this lesion by less invasive techniques is important to avoid an unnecessary surgical procedure. We report a case of a one-month-old male infant who presented with a firm 3 cm swelling on the left side of the neck. Fine needle aspiration was performed and the cytological features were suggestive of fibromatosis colli. Fibromatosis colli has to be differentiated from various congenital, inflammatory and neoplastic conditions that can occur in a similar location. Fine needle aspiration cytology appears to be a cheap, rapid, less invasive and fairly accurate diagnostic aid for excluding other causes and detection of this type of lesion. Identification of these lesions is important as they are usually self-eliminating with some cases requiring conservative management and rarely surgical intervention.