ObjectivesThis study aimed to establish the reference intervals (RIs) of thyroid function test among the adult Sudanese population in Khartoum, Sudan. A multi-stage survey stratified sampling method was used. Total triiodothyronine (TT3), total thyroxine (TT4) level and thyroid stimulating hormone (TSH) levels were measured using radioimmunoassay gamma counter (Riostad, Germany) to determine the reference intervals.ResultA total of 390 adults aged 20–75 years (male: 40.5%, female: 59.5%) were recruited. The median (95% intervals) serum TSH, TT4 and TT3 levels were 1.2 (0.50–3.1) mIU/L, 103.0 (63.0–159.0) nmol/L and 1.4 (0.8–2.7) nmol/L respectively. Compared with males; females had significantly lower TSH level and significantly higher TT4 level, but there was no significant difference when the TT3 level was assessed. While there was no significant difference in the level of TSH and T3 in the age group, T4 levels have shown a progressive increase with age. In summary the RIs for TSH, TT4 and TT3 in this setting were different from the levels provided by the manufacturers. A significant different was observed in TSH and FT4 when considering gender issue. The RIs were not different in the different age groups except for FT4.