We assessed effects of forearm bands on three species of horseshoe bats (Rhinolophus ferrumequinum, R. euryale and R. mehelyi) marked for studies on regional movements and colony structure in Northern Bulgaria. Overall, more than 85% of the 580 recaptured individuals showed no negative impact of the banding. We had to note, however, slight or severe injuries in 7.6 and 6.4% of the bats, respectively. Injury rates varied greatly according to species and ring sizes. The use of the smaller of two tested ring sizes caused major injury rates of more than 60% of the recaptured R. mehelyi. But even in R. ferrumequinum, for which we obtained the largest sample size, and for which the recommended ring size is well-established, carefully fitted forearm bands caused injuries in 9.3% of the recaptures, an injury rate that is much higher than in most vespertilionid bat species. The main reason for the sensitivity of the horseshoe bats to ringing was that the ring rubbed raw the bats' propatagium; the resulting injuries led to growing scars and infections. We compare published and unpublished injury rates of 28 bat species with our results and discuss the use of alternative marking methods. We suggest that banding of horseshoe bats should be limited to well defined projects and only used if the study populations are in a good preservation condition and long term effects of the marking method can be monitored.