Malnutrition, particularly undernutrition among preschool children, is a critical global health concern with profound implications for child health, growth, and development. This study examines the prevalence and grades of thinness in preschool children aged 2-5 years in the culturally diverse region of Paschim Medinipur, West Bengal, conducted within eight ICDS centers in seven villages under Medinipur Sadar Block, with 215 participants (105 boys and 110 girls). Body mass index (BMI) was calculated, and thinness was classified into Grades I, II, and III for mild, moderate, and severe cases, using age- and sex-specific BMI cutoffs proposed by Cole et al, 2007. The findings highlighted significant trends: boys had higher mean height, weight, and BMI values than girls. Both exhibited an overall pattern of increasing height and weight and decreasing BMI with age, with exceptions among 4-year-olds. Thinness was prevalent, affecting 61.9% of boys and 62.7% of girls, with the lowest prevalence among 5-year-olds and the highest among 3-year- olds. Grade III thinness was the most common category, impacting 28.4% of boys and girls, followed by Grade I (18.6%) and Grade II (15.3%). Notably, no significant association between sex and thinness prevalence was found, underscoring the similar risks boys and girls face regarding undernutrition. The present study revealed that the nutritional status of these villages’ preschool children was poor, with a very high rate of thinness present among both sexes. These results indicate that the present food supplementation program of the ICDS centers needs to be improved.