A partial trisomy 13q was observed in siblings with hexadactylia, hypertelorism, haemangiomata and severe psychomotor retardation. It originated from a maternal inversion translocation 46,XX,inv(8)(q23q241),t(8;13)(q241;q32). The family showed a pedigree pattern typical for the segregation of a chromosomal translocation. In spite of this the diagnosis was delayed several years, because the bands involved from the two chromosomes were of great similarity. This stresses the importance of reinvestigating families with a clinical suspicion of a chromosomal syndrome, preferentially with prometaphase chromosomes. The identification of a chromosomal rearrangement is essential for genetic counselling and prenatal diagnosis.