Problems in reporting results of nestbox studies, apart from those covered by Lambrechts et al. (2010. Acta Ornithologica 45; 1–26), are discussed. The papers resulting from nestbox studies mostly fail to provide essential data on breeding densities, nest predation rates, nest soaking, ectoparasites, and brood productivity. The fact that the nestbox plots constitute large scale, long lasting field experiments is usually not acknowledged, and the consequences of experimental conditions for the external validity of results are not assessed. Unqualified inferences on the adaptive value of ecological and behavioural characteristics are often made. To remove these shortcomings, every nestbox study should include detailed descriptions of the types, sizes and distribution of breeding boxes used, effectiveness of nest predation and flood prevention, and breeding densities (all in the methods section); and a discussion of (1) how conditions in the study area differed from the reference conditions (with tree holes), (2) what could be the impact of these modified conditions on the outcome of study, and (3) what is external validity of the results.