BACKGROUND In children, innate and adaptive immunity varies with age, disease status, and ethnicity, reflected by lymphocyte subsets and serum immunoglobulin (Ig) levels. The paucity of such data from the Indian subcontinent necessitated this study. OBJECTIVE This study aims to determine reference ranges of Ig and lymphocyte subsets in Indian children from birth to 5 years. METHODS Neonates, infants, and children from a tertiary care hospital were selected and categorized into 5 groups from cord blood/newborn to 5 years. METHODS Samples were taken from cord blood and healthy children up to 5 years of age. Complete blood counts, serum Ig levels (by turbidimetry), and lymphocyte subsets (by flow cytometry) were studied, and reference ranges calculated. RESULTS Four hundred and three samples were analyzed; 53 from cord blood and 350 from children 1 month to 5 years. High IgG levels were noted at birth, which decreased in the first 6 months followed by a rise thereafter. IgM remained low in infancy and peaked at 13-36 months. IgA levels were very low at birth but increased with age. CD4 counts were high in cord blood till 3 years of age and then declined. CD8 and CD19 counts remained steady till 5 years of age. CD56 increased after the age of 2 years. CONCLUSIONS While our data correlated well with published literature, notable differences were higher IgM levels seen in 1-3 years' age group and higher natural killer cells through all age groups in our study. Our results provide the largest database of its kind from our country.