We conducted a retrospective study of 53 mastoidectomies in 51 patients with acute otomastoiditis. In 26 cases (49.1%), surgery had been performed within 48 hours of the development of symptoms. The most common complication of acute otomastoiditis was subperiosteal abscess, which occurred in 37 cases (69.8%). Intracranial complications were seen in 6 cases (11.3%). The most common pathogens isolated from subperiosteal abscesses, the mastoid cavity, and intracranial collections were Streptococcus spp and Staphylococcus aureus. In 14 cases (26.4%), conservative treatment failed to cure acute otomastoiditis; such cases should raise a suspicion of a subperiosteal abscess, an underlying cholesteatoma, or an infection caused by gram-negative bacteria. Upon hospital admission, patients should receive antibiotics that are effective against both gram-positive and gram-negative organisms. Patients with intracranial complications or facial nerve paralysis may require a combination of two or more antibiotics. Long-term follow-up is highly recommended.