Background Hypogammaglobulinemia is common in infant humoral lmmunOdeficlencles and has complicated causes and outcomes We almed to determlRe the clinlcal manlfestations lmmunologlcal changes and outcomes of Shanghal lnfants with hypogammaglobulinemia Methods Patients under 2 years old, having one or more warning signs of primary immunodeficiency disorders, serum immunoglobulin levels below the lower llmlt of reference range per age and with normal numbers for lymphocyte subsets were analyzed and followed uP for 2 to 3 years Results A total of 91 chlld ren fmale-to-female ratio: 2.25: 1) pa rticlpated in the study. 1nltial clinlcal presentation was recu rrent upper respiratory tract infection(46%), invasive infection(3%), atopic disease(32%)IgA reduction(77%)was prevalent; 34% patients had more than one isotype reduced Du ring follow-up, 51 of 62 patients(82.25%)had lmmunoglobulins normalized at the age between 12-48 months; these were dlagnosed as transient hypogammaglobulinemia of infancy (THI)Long-term follow-up may reveal a diagnosis for the remaining 11 infants with persistent lower lmmunoglobulin levels who dld not have antlbody titers measu red Earlier onset was correlated with higher rates of normalization More patients were diagnosed with isolated hypogammaglobulinemia in 2006 compared with the prevlous 4 years (2002-2005) Conclusions The awareness of lmmunodeficiency among pedlatricians has been greatly lmproved Recu rrent otitis medla was not a major lnfection ln our patients THl ls a relatively common condltion associated with lnfant hypogammaglobulinemia Inthe absence of specific antibodytiters, the diagnosis ofTHI can be confirmed retrOspectlvely with lg levels normalized ln follow-uP vlsits Therefore long-term follow-up and frequent re-evaluation of these patients are necessary to dlstingulsh them frOm true prlmary lmmunodeficiency