In 2006 Enzyme Replacement Therapy (ERT) with alglucosidase alfa was registered as a treatment for Pompe disease. We present a primiparous 40-year-old woman with adult-onset Pompe disease who continued receiving alglucosidase alfa in a dose of 20 mg/kg every other week during pregnancy and lactation. The patient had moderate limb-girdle weakness and used nocturnal ventilation. The mother's clinical condition remained stable until the 25th gestational week. Thereafter she experienced more mobility problems and increased respiratory effort. Fetal growth was normal as monitored by regular ultrasound investigations. At a gestational age of 38 weeks and 5 days, a healthy baby-boy was born. There were no maternal complications and the child developed normally. After delivery pharmacokinetic studies were performed in breast milk and plasma. In breast milk, alpha-glucosidase activity levels peaked 2 hours after the end of the infusion, which was 2 hours later than in plasma. The alpha-glucosidase activity in breast milk disappeared over a period of 24 hours after the infusion. This case report indicates that ERT with alglucosidase alfa can be administered safely during pregnancy. We recommend refraining from breastfeeding on the day of the infusion, since Alglucosidase alfa transfers in small amounts into breast milk. Conflict of Interest declared.