With an increase in travel to tropical countries, the need to improve the disease-risk perceptions of travelers who are either naive or given inappropriate or ineffective advice is becoming increasingly important. More widely available, specialized centers that can provide advice on tropical or travel-related diseases have been established, but their efficacy on travelers' knowledge and health has not been verified. Therefore, this study was undertaken to evaluate the impact of the service provided by a routine travel consultation at the Hospital for Tropical Diseases Travel Clinic, London, England. Self-administered questionnaires were given to 161 preconsultation and 144 postconsultation clients. The consultation included an interview covering travel plans and immunization and medical history, and advice was given on the journey, necessary immunizations, and prophylaxis. Data were analyzed using the Statistical Analytic System software and the mean differences in knowledge between pre- and postconsultation scores were correlated using the nonparametric Mann-Whitney procedure. The control of mutually confounding factors was maintained by multiple regression using the Mantel-Haenszel summary chi-square and the General Linear Model procedures. Comparison of the entry and exit scores showed a significantly improved overall knowledge of travel-related diseases in the exit, postconsultation group. Subanalysis revealed that this difference was due to an increased knowledge of malaria and its prevention and perceived risk of cholera. Knowledge about the management of diarrhea or fever, however, was not significantly improved by a consultation. Inexperienced travelers taking packaged or organized trips, and those from socioeconomic groups I and II showed the largest increase in knowledge following consultation. Our results show that a face-to-face interview for an average of 18 minutes by trained staff is an effective way of improving travelers' knowledge on certain topics. The slight improvements overall are explained by the levels of experience of travel and previously acquired knowledge of the clients in our study. Effective advice on malaria prevention and some health risks is given during an average consultation; however, there is still a need for improvement in giving information on the management of diarrhea, fever, and other travel diseases.