To the Editor-In his letter, Dr Tomassi describes his study from Kaiser Permanente Southern California, in which the investigators "expectantly managed" 378 patients with high-grade anal dysplasia, demonstrating an incidence rate of 0.19% per patient-year for anal squamous cell carcinoma (SCC). This rate is lower than the rate we identified using the population-based cancer registries of the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute. It must be emphasized that Dr Tomassi's data derive from Kaiser Permanente billing codes, and therefore all included patients are medically insured. As Dr Tomassi states in his letter, surveillance of patients at high risk for anal SCC is provided by "general and colorectal surgeons, infectious disease specialists, family medicine and internal medicine physicians, and gynecologists." The Kaiser Permanente data come from a large integrated managed care group that receives high marks for quality of care with an emphasis on preventive care and access to care. This likely represents a higher level of longitudinal care than most patients in the United States are fortunate enough to receive. Our SEER data are derived from 34.6% of the US population, irrespective of insurance status, and are Data from different sources have different applications: for a large healthcare system or insurance organization looking to allocate resources and determine policy for a population, we commend the use of the Kaiser data. For a surgical practitioner counseling his or her patients, we commend data such as our own. We share with our crosstown colleagues the clinical conclusion that expectant management of HSIL is reasonable, based on evidence and experience. We wonder if we can now call it San Diego rather than expectant management, to use a sunnier and less pregnant term! We also share with everyone in the field, including advocates of HSIL ablation with whom we disagree, the conviction that people at high risk for anal cancer should be followed regularly by practitioners accustomed to examining the anus. Indurated or ulcerated lesions should be biopsied so that early stage cancers can be detected and cured.