To determine the optimal timing of the introduction of complementary foods and their impact on the health status of infants during the first year of life, a study was conducted on the basis of 7 children’s clinics in the city of St. Petersburg. Materials and methods. At stage I, there was conducted a random survey of 534 mothers, whose infants received breast milk up to a year and later. At stage II, the data on the child’s health groups were copied from the account form 112 /U “History of the development of the child”. Results. 81.1% of mothers were found to begin to give vegetable complementary foods at the age of 4-6 months. Vegetable puree was given to children of health groups I and II on time, as well as to children who have chronic diseases at the stage of compensation (health group III). For children with chronic diseases at the stage of sub- and decompensation (IV and V health groups), vegetable complementary foods were introduced into the diet after the recommended period. 71.5% of mothers gave grain complementary foods on time, 24.5% - later. In all children, regardless of health group, most mothers introduced porridge into the diet in a timely manner. Most mothers introduced mashed potatoes, as well as other protein products, including cottage cheese, egg yolk, and mashed fish later regardless of the state of health of the child. 24.9% of mothers introduced meat puree, 22.8% women cottage cheese, 30.0% egg yolk, and 17.9% fish puree earlier. The majority of mothers did not introduce fermented milk products on time: only 35.5% of mothers started introducing them on time, 46.8% - later. 61.4% administered whole milk earlier, and mothers introduced it into the diet of healthy children (I and II health groups) at the prescribed time, and in children with chronic diseases (III-V groups) later than recommended. Conclusion There is a relationship between the state of the child’s health and the timing of the introduction of complementary foods: vegetable puree and whole milk, children with chronic diseases are introduced later.