Carbohydrate deficient glycoprotein syndromes (CDG) are inherited multisystem disorders characterized by the abnormal glycosylation of a number of serum glycoproteins. CDG-Ia results from deficiency of phosphomannomutase that catalyzes the conversion of mannose-6-phosphate to mannose-1-phosphate in the cytosol. We report a case of CDG-Ia in an 11-month-old girl with developmental delay, failure to thrive, inverted nipples and abnormal fat pads. The abnormal pattern of transferrin glycosylation and phosphomannomutase activity assay confirmed the diagnosis of CDG type Ia. Unfortunately, an efficient treatment is still not available for CDG type Ia patients. This is the first report of a Taiwanese patient with this syndrome.