The composition of nestling diet in the red-breasted flycatcher Ficedula parva was studied by videotaping 14 broods, in natural stands of the Białowieża Forest, in relation to nestling age and the sex of the parents. On average 51.5% of the prey items were flying insects, 25.9 % spiders and 22.8% caterpillars. Amongst flying insects, Diptera dominated (84.8%), then Lepidoptera (7.6%) and Orthoptera (6.6%). The composition of the diet changed significantly in relation to the age of the nestlings. The proportion of caterpillars decreased with nestling age from 36% to 13%, whilst that of flying insects increased from 42% to 64% and spiders achieved their highest representation in the middle stages of nestling development. Within the group of flying insects, composition of prey types also changed significantly: the proportion of Orthoptera increased from 7% to 11%, and Lepidoptera decreased from 9% to 3%, while the proportion of Diptera was almost unchanged. No differences were found in general in the proportions of prey types provided by males and females, although they differed in respect to nestling age. In the first five days of nestling life, males provided more caterpillars and fewer flying insects than when nestlings were older.