Secondary sexual characters are large structures of great intricacy of design, and there are many ways in which their development can be disrupted. Both somatic and germ-line mutations affecting the expression of secondary sexual characters are likely to be biased and most frequently reduce performance because of the great complexity of characters. I investigated the degree of fluctuating asymmetry and the incidence of aberrant secondary sexual characters in the monogamous barn swallow Hirundo rustica in two areas in Ukraine, one near Chernobyl, and the other near Kanev. I predicted that developmental disorders should be more frequent in a recent sample of birds from the Chernobyl area than in samples from other areas, and than in museum samples pre-dating the 1986 contamination event. There were apparently no consistent effects of area or time period on the morphology of barn swallows. The level of fluctuating asymmetry in male tail length was considerably elevated in the Chernobyl area in the recent sample, but not in females, and three other morphological variables were unaffected in both sexes. Males with high degrees of asymmetry in their tails bred later than symmetric males. The incidence of aberrant feather morphology in the Chernobyl area was higher for tail ornaments of males than for other morphological characters in males, and than for the homologous character of females, and there were no cases of aberrant feathers in the control area or in the museum samples. Males with aberrant tail feathers bred later than other males.