Psychiatric disorders following treatment with Mefloquine were described several times since the introduction of this antimalarial drug in Germany in 1985. On the basis of two case reports problems of the diagnosis and of the correlation of psychiatric disorders with the medication are discussed. Particularly are an analysis of the development of the ADR and a comparison of the psychiatric symptoms with known ADR-cases and with other psychiatric diseases important. This seems to be significant for an optimal treatment as well as for the assessment of the prognosis.