To better characterize infants presenting with diminished immunoglobulin levels and intact antibody formation, we present 49 such infants, correlating presenting characteristics with history and time to immunoglobulin normalization. Term infants with the following characteristics were included: 1) one or more immunoglobulin classes > 2SD below mean, 2) protective antibody titer to tetanus and diphtheria, 3) intact cellular immunity, 4) no features of other syndromes. The children were 69.4% male and had recurrent otitis media (77.6%), wheezing (61.2%), and atopy (26.5%). Diminished IgA (95.9%) was most common, but 65.3% had multiple isotypes diminished. During follow-up, 25/49 (51%) normalized immunoglobulins, of whom 80% were male; only 48% normalized in infancy. Female immunoglobulin normalization was significantly delayed (p < .001). No deaths or serious infections occurred. This phenotype is predominantly seen in male infants with otitis media and wheezing. Female infants have significantly delayed immunoglobulin normalization. Transient hypogammaglobulinemia of infancy can be diagnosed only retrospectively.