Lithium is frequently used in the management of several psychiatric disorders including acute mania, bipolar (manic-depressive) disorder, and recurrent depression. We describe a patient in whom hidradenitis suppurativa developed while the patient was receiving lithium. The cutaneous side effects of lithium are reviewed. The most frequent are psoriasis, acneiform lesions, folliculitis, alopecia, and a maculopapular/macular eruption. Many of these side effects respond less readily to conventional therapy while the patient is receiving lithium.