To investigate the short- and long-term impacts of adenoidectomy with/without tonsillectomy on the immune functions of young children < 3 years of age.This longitudinal prospective study included 40 pediatric patients (age <3 y) undergoing adenoidectomy with/without tonsillectomy for snoring and sleep apnea. Serum immunoglobulin IgA, IgG, IgM, complement C3, and C4 levels were measured for the status of humoral immunity; CD3+, CD4+, CD8+, CD4+/CD8+, CD19+, CD56+, CD3+CD4-CD8-, and CD3+CD4+CD8+ T cells were measured for the status of cellular immunity. Blood samples were taken at 3 time points: before surgery, 1 month after surgery (short-term), and 3 months after surgery (long-term). All patients were assessed for short-term outcome at 1-month postoperation, but only 30 patients were followed at 3 months after surgery. The incidence of recurrent respiratory tract infections and other immune-related conditions were recorded at each follow-up.The levels of IgA significantly decreased from the preoperative level at 1-month follow-up (P < .05), but still within normal range. No significant changes were found in the levels of IgA, IgG, IgM, C3, C4, CD3+, CD4+, CD8+, CD4+/CD8+, CD19+, CD56+, CD3+CD4-CD8-, and CD3+CD4+CD8+ T cell at 3-month follow-up in comparison with preoperative levels. There was also no episode of recurrent respiratory tract infection and other immune-deficiency conditions.Adenoidectomy with/without tonsillectomy may result in a reduction in individual antibodies in children <3 years of age, but did not show negative impacts on their immune functions. Also, the surgery does not lead to the increased risk of upper respiratory tract infection in these children.