A large number of studies have demonstrated that habitat characteristics have a huge impact on all aspects of animal life history. This hypothesis predicts a relationship between habitat structure and the main components of fitness and, consequently, also predicts a relationship between habitat structure and other traits indirectly related to fitness, such as condition or health. We tested whether there was any relationship between the characteristics of a pine forest in the Iberian Peninsula and the condition of Great Tit nestlings reared in that forest. The parameters used to estimate nestling condition were weight, haematocrit and the presence of haemoparasites. The results suggest that mature forests produced nestlings in better condition but with a higher prevalence of haemoparasites than young forest, possibly because mature forests are a good habitat for both the bird and the parasite vector.