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Family studies in developed countries show an increased prevalence of thyroid autoantibodies in first degree relatives of children with autoimmune thyroiditis (AIT). Such data is scarce from developing country setups. Materials and Methods: Thyroid profiles and autoantibodies were evaluated in 50 first degree relatives of 50 children with AIT. Results: Eleven (22%) subjects had raised thyroid stimulating hormone (TSH); 4 fathers (42.5%), 3 mothers (12%), 1 brother (33%) and 3 (23%) sisters. Three (6%) showed thyroid profiles consistent with hypothyroidism. Levels of triiodothyronine (T3) were raised in 7 (28%) mothers and 2 (15.4%) sisters while 2 (8%) mothers and 3 (23.1%) sisters also had increased thyroxine (T4) levels; none had low TSH or clinical evidence of hyperthyroidism. Anti-thyroid peroxidase (TPO) antibodies were positive in 9 (18%) subjects; 4 mothers (4/25, 16%) 3 fathers (3/9, 33%) and 2 sisters (2/13, 15.4%). Mean T3 levels were lower, mean T4 were similar and mean TSH levels were higher in TPO-positive as compared TPO-negative subjects. Anti-Tg antibody positivity was found in 32 (64%) subjects; 14 (56%) mothers, 7 (77.7%) fathers and 11 (84.6%) sisters. Mean thyroid hormone levels were similar in Anti-Tg positive and negative subjects. Two (8%) mothers, 1 (7.7%) sister and 2 (22.2%) fathers had both antibodies in their serum; their thyroid profiles were similar to subjects with anti-TPO positivity. Conclusions: Thyroid dysfunction is present in first degree relatives of North Indian children with AIT. Anti-TPO antibodies are less common but have strong correlation with thyroid dysfunction. Conversely, anti-thyroglobulin (TG) antibodies are commonly detected but correlate poorly with thyroid dysfunction. [ABSTRACT FROM AUTHOR]