A recent study by Wellmann et al (Blood. 2000;96:398-404) detected clusterin expression in all 36 systemic anaplastic large cell lymphomas (ALCLs) tested, but not in any of 9 primary cutaneous ALCLs. Our purpose was to confirm the diagnostic usefulness of clusterin in systemic ALCL and to evaluate its efficacy in distinguishing primary cutaneous ALCL from secondary skin involvement by systemic ALCL. We examined clusterin expression by paraffin immunohistochemical analysis in 41 systemic ALCLs (18 ALK-1+ and 23 ALK-1-), 9 primary cutaneous ALCLs, and 4 secondary cutaneous ALCLs. Clusterin was positive in 95% of systemic ALCLs (39/41), including 100% (18/18) of the ALK-1+ cases and 91% (21/23) of the ALK-1- cases. Five (56%) of 9 primary and 3 (75%) of 4 secondary cutaneous ALCLs were positive for clusterin. Our observations confirm the diagnostic usefulness of clusterin in systemic ALCL, especially in the ALK-1- cases. However, our data fail to demonstrate its value in distinguishing primary from secondary cutaneous ALCL.