There are few data in the literature reporting the evolution of hypogammaglobulinemia in premature and full-term infants during the first years of life. The aim of this study was to assess the clinical and immunological evolution of premature and full-term infants with hypogammaglobulinemia. We included 24 children (11 premature and 13 full-term infants), aged 0-36 months, with hypogammaglobulinemia. Fifteen (62.5%) children had an isolated reduction in IgG, 7 (29.2%) had a decrease in both IgG and IgA and 2 (8.3%) a reduction in IgG and IgM. Normalization of IgG serum levels occurred in the premature infants at a mean age of 7.2 months. Full-term infants were divided into 3 groups based on age at normalization of IgG serum level: A) hypogammaglobulinemia with normalization within 12 months of life; B) with normalization within 36 months of life; C) normalization after 36 months. All the premature infants with hypogammaglobulinemia recovered, even though in the lower limits for age in the first years, while transient hypogammaglobulinemia observed in full-term infants has a different age of recovery.