Caution: prenatal clubfoot can be both a transient and a late-onset phenomenon.

Clubfoot (talipes equinovarus) is a common orthopaedic malformation that can be accurately diagnosed prenatally. The study was conducted to investigate possible in utero visualization of transient and late-onset clubfoot. Early (13-16 weeks' gestation) prenatal transvaginal sonographic diagnosis of clubfoot deformity was made in 36 cases during the study period. Only those cases where follow-up examination revealed different sonographic findings were considered. The results showed that seven cases of transient (as well as relapsing) clubfoot were identified. In 4 of 7 cases, the clubfoot resolved (all after more than 10 min of observation) during the same examination. In the fifth and sixth cases, it initially resolved, later reappearing in follow-up examinations (20 and 22 weeks' gestation). In the seventh case, the clubfoot persisted for two consecutive examinations (2 weeks apart each) and later disappeared. In addition, six late-onset (22-24 weeks' gestation) clubfoot cases were identified during the study period. Although infrequent, in utero clubfoot can be both a transient and a late-onset phenomenon. Over- and under-diagnosis are potential hazards in these situations.