Passive integrated transponders (PITs) are increasingly used to study behaviour in small passerines. However, to ensure the reliability of such studies, knowledge of long-term fitness consequences of equipping passerines with PITs is crucial. We quantify the effects of fitting PITs, injected subcutaneously or glued to colour rings, on fitness in house sparrows Passer domesticus. Relative annual fitness was assessed with the delifing method as an individual's annual contribution to population growth rate. We found no evidence for adverse fitness effects in individual birds fitted with PITs compared with individuals without PITs, independent of the methods of fitting the tags. Our results provide a solid basis for the assumption that such logging devices are safe to use in small passerines and that PITs will most probably not affect the outcome of studies with respect to population dynamics and fitness components.