Pericentric inversions ascertained by the majority of French cytogenetics laboratories are collected and analysed. The whole sample is composed of 305 independent cases, most of which unpublished previously. inv(2)(p1200q14.100) = 87 probands, inv(5)(p1400q1400) = 22 probands, inv(10)(p11.22q21.109) = 17 probands, and inv(10)(p1209q11.109): 12 probands are the most recurrent. The risk of aneusomie de recombinaison varies from .00 to .10 in the progeny of inversion carriers, depending on the location of the breakpoints. The risk of other chromosome imbalances may be increased by a factor of 3, and that of abortions by a factor of 2. A reduction of fertility is likely to exist in male carriers, especially when large chromosomes are involved. In most instances, the apparent preferential segregation of the inverted chromosome may be due to ascertainment biases, but such segregations may exist for some recurrent inversions. Endogany may also explain recurrence, such as that of inv(2)(p12q14.100) which is observed mostly in the Jewish community originating from Spain before inquisition time and from North Africa.