Abstract. OBJECTIVE: A cross-sectional study was done to assess the size of thymus in term healthy infants using sonography and to assess its variation in size, shape, location, echogenicity and echotexture for both male and female reference population. MATERIAL AND METHODS: A total of 250 term healthy neonates of either sex were subjected to thymic sonography. The shape, size in maximal anteroposterior, longitudinal, and transverse dimensions of both right and left lobes of thymus was evaluated. Their echotexture and echogenicity were determined and standards for reference population were calculated. The results were statistically evaluated. RESULTS: According to the shape; the thymus was quadrilateral in 156 neonates (62%), round in 37 (15%), bilobate in 32 (13%), and crescent shaped in 25 (10%) in transverse scan. According to the echo texture, the thymus echogenicity was homogeneous and almost similar or slightly less to that of the liver and spleen in most cases 200 [80%] and was coarse in 50 (20%). In all subjects, the echogenicity of the thymus was less than that of the thyroid gland. Variations in location of the thymus were found in 70 (28%) neonates. The range of mean AP diameter was 0.39–2.36 cm (mean 1.43 ± 0.3), that of transverse 1.4 – 4.3 cm (mean 2.16 ± 0.54) and that of thymic index 1.2–5.1 cm2 (mean 2.98 ± 0.64). CONCLUSIONS: A normative range was calculated for standard population, which can be used as a reference for comparing thymus size for both normal and diseased neonates for various immunological diseases.