The breeding period, a key stage in animal life histories, incurs high energy expenditure and there is often the possibility that parasite infections may compromise its success. Since defences against parasites are also costly to produce, individuals should optimise the allocation of limited available resources to reproduction activities or self-maintenance, e.g. supporting immune function and sustaining body mass. Here we explored the relationships between haemosporidian infection status, body condition and nestling feeding rate in helpers, female breeders and male breeders of a cooperative breeding corvid, the Iberian (Azure-winged) Magpie Cyanopica cooki. For infection status we differentiated between uninfected birds and, separately, those infected with one or more than one Leucocytozoon parasitic lineage. Our predictions were that both breeder and helper Iberian Magpies harbouring a haemosporidian mixed-infection should show lower body condition and nestling feeding rates than single-infected and uninfected birds. We found that most of the Iberian Magpies studied (78.7%) were infected with Leucocytozoon species, most of them (67.1% of Leucocytozoon-infected individuals) harbouring mixed infections. The scaled body mass index did not differ with respect to infection status in male or female breeders; however, mixed-infected helpers showed lower body condition than single-infected ones. Moreover, we found that mixed-infected males, as well as single and mixed-infected female breeders, but not infected helpers, showed lower nestling feeding rates than uninfected individuals. These findings could indicate a compromise between reproductive and immune functions in the Iberian Magpie, which effect becomes more evident in those individuals with a higher reproductive investment during the breeding period. —Parejo-Pulido, D., Magallanes, S., Vinagre-Izquierdo, C., Valencia, J., de la Cruz, C. & Marzal, A. (2021). Relationships between haemosporidian infection and parental care in a cooperative breeder, the Iberian Magpie Cyanopica cooki. Ardeola, 68: 163-180.