In this report, we present the cytogenetic findings in an adult female patient with lymphomatoid papulosis (LyP) type A, a cutaneous lymphoproliferative disorder with possible progression to lymphoma. Karyotyping of the CD30+ atypical lymphoid cells revealed numerical and structural aberrations. Trisomy 7, a common finding in hematologic disorders such as adult T-cell leukemia and non-Hodgkin lymphomas, was detected. Additionally, a breakpoint was found at 10q24 in the region of the TCL3 oncogene. These results contrast with cells of a young female patient (age 3) with a type A LyP, which showed a normal karyotype as well as cells of a male adult with type B LyP. None of the cases showed the t(2;5)p(23;q35) common in CD30+ anaplastic large cell lymphomas, which can closely resemble LyP. Our findings are discussed in the context of the literature concerning the histology, immunophenotyping, and cytogenetics of LyP. Together the results suggest different steps in the development of LyP and distinct forms of this one disease.