The authors describe a case of unilateral adrenal abscess in a neonate, which was diagnosed at 13 days of age by abdominal ultrasonography. The newborn presented with persistent high white blood cells after Proteus mirabilis omphalitis. Magnetic resonance imaging and needle aspiration confirmed the diagnosis. This is the second case of Proteus mirabilis neonatal adrenal abscess reported in the literature. Percutaneous drainage allowed complete recovery.