The purpose of this study was to estimate the health burden imposed by Lyme disease (LD) in Maryland during 1992 and 1993. A cross-sectional 1-in-1S survey of physicians (total, 1200) in Maryland was conducted to estimate the incidence of diagnosed LD, presumptive cases of LD, patients with tick bites, and diagnostic tests ordered for LD. Results show that LD is underreported by 10- to 12-fold in Maryland, that 80% of cases are managed by primary care physicians, and that there is discordance between the actual clinical treatment of patients and the recommended approach. In addition, the much greater numbers of patients treated for presumptive LD, seen and given prophylaxis for tick bites, and having diagnostic tests indicate that real and perceived LD is a far greater public health problem and uses more medical resources than official surveillance data suggest.