Preening is a type of feather maintenance behaviour in birds, that fulfils an important role in grooming. Preening may also be important for signalling quality of mates. Therefore we hypothesized that the frequency of preening may be related to sex and population density of White Stork Ciconia ciconia. We observed preening activity of 25 pairs in Western Poland at the beginning of incubation, when preening frequency is the highest. Birds were observed on the nest, because most preening behaviour occurs there. We found that being on the nest males spent proportionally more time on preening than females (on average 30% vs. 16%). Females spent more time preening when their mate was present at the nest. There was no significant relationship between preening frequency and indirect quality indicators (arrival date, laying date, hatching date, clutch size, brood size) nor between the distance to nearest neighbours and the time males and females spent on preening.