A randomized clinical trial was undertaken to compare clinical and serologic parameters of the efficacy of one-dose azithromycin in the prophylaxis of Mediterranean spotted fever (MSF) in 122 persons with a tick bite history. Antibodies to Rickettsia conorii (R. conorii) were detected by indirect immunofluorescence (IFA) assay in 55 (45.1%) of 122 subjects. Positive result was obtained in 19 (31.1%) of 61 subjects with azithromycin prophylaxis and in 36 (59.0%) of 61 subjects without prophylaxis. Clinical signs and symptoms of MSF were recorded in 6 (9.8%) and asymptomatic infection in 30 (49.2%) of 61 subjects without prophylaxis. In subjects with prophylaxis, clinical signs of the disease were not recorded at all, whereas asymptomatic infection was detected in 19 (31.1%) of 61 subjects. Based on the results obtained in our study, we assume that a single dose of azithromycin is promising in MSF prevention.