Adenomyomatosis of the gallbladder is defined as hypertrophy of the gallbladder mucosal epithelium that invaginates into a thickened muscularis propria, leading to the formation of intramural diverticula. It is typically considered a benign condition most commonly affecting adults and, rarely, children. In this case report, we present a case of gallbladder adenomyomatosis in a 3-month-old infant. The diagnosis was made incidentally on ultrasound examination of the abdomen, in an otherwise asymptomatic child with no laboratory test abnormalities and no underlying disease. The purpose of this case report is to make infantile adenomyomatosis and its implications known to clinicians, as the literature on this topic is limited. To the best of our knowledge, this is the youngest reported case of adenomyomatosis in the pediatric population.