Cytogenetic analysis revealed structural rearrangements of 11q13-21 in 9 lipogenic tumors--4 hibernomas, 4 typical lipomas and 1 mixed myxoid and well-differentiated liposarcoma. Two hibernomas and all lipomas simultaneously showed aberrations attributable to previously recognized cytogenetic subgroups among benign adipose tissue tumors, i.e., supernumerary ring chromosomes or rearrangements of 6p, 12q13-15, or 13q. The sole anomaly in the liposarcoma was a 4-way translocation t(9;11;22;12)(q21;q13;q11;q13), an aberration that has not previously been detected in either myxoid or well-differentiated liposarcomas. Together with our 4 cases, a total of 7 cytogenetically aberrant hibernomas have been reported. Five tumors have shown rearrangements of 11q13 and 2 of 11q21, indicating that this segment of chromosome 11 harbors one or more genes of importance in hibernoma development. Rearrangements of 11q13-21 also appear to be frequent in typical lipomas; a total of 8 typical lipomas with 11q13-21 changes have been described, including those in our series. In all but 1 however, breakpoints were also found in 6p, 12q13-15, or 13q.