The availability of uniform and precise criteria for disease evaluation, response to treatment, and clinical staging of Kaposi's sarcoma (KS) in individuals with the acquired immune deficiency syndrome (AIDS) would facilitate therapeutic trials in patients with this neoplasm. Recently, a group of oncologists conducting clinical trials in patients with AIDS-associated KS as part of a cooperative group established by the National Institute of Allergy and Infectious Diseases (NIAID) drafted such criteria. The criteria take into account the unique problems associated with the evaluation of patients with a disseminated cutaneous neoplasm in the setting of a systemic virus infection associated with immune deficiency. The recommendations include a standardized format for documenting the extent of KS on initial and subsequent evaluations, response definitions that include assessments of lesion nodularity and tumor-associated edema in addition to more traditional methods for evaluating tumor response, and a new staging system that includes extent of tumor, immune status, and other AIDS-related disease manifestations, akin to the tumor-node-metastasis (TNM) system used to stage other tumors. The adoption of standardized criteria for the evaluation of KS should prove useful for group trials and for other investigators involved in the treatment of this disease.