OBJECTIVE To compare results on the Autonomy Preference Index (API) and the Health Opinion Survey (HOS), two instruments that measure patient desire for information and involvement in decision making. METHODS Cross-sectional survey. METHODS University-based primary care outpatient longitudinal and acute care clinic. METHODS 167 patients with benign prostatic hyperplasia, back pain, or mild hypertension seen from October 1991 to December 1992. RESULTS On the API and the HOS (both scaled from 0 to 1), the patients had intermediate desire for involvement in decision making (median API: 0.42; HOS: 0.36) and higher desire for information (median API: 0.97; HOS: 0.57). With either instrument, the desire for information exceeded that for involvement in decision making (p < 0.0001). The API information scores were higher than the HOS information scores (p < 0.0001), probably because the HOS focuses on patient behavior rather than desire. Variation in desire for information and involvement in decision making was substantial and largely unexplained. CONCLUSIONS Most patients have a high desire for information, the desire for information and involvement in decision making varies substantially among patients, and the API is preferable to the HOS for researchers interested in focusing solely on patient desire for information.