Lassa virus (Arenaviridae), is the etiological agent of Lassa fever, a severe human disease with high mortality rates for hospitalized patients. Lassa fever can be difficult to distinguish clinically from other viral hemorrhagic fevers. The virus is initially spread to people via contact with urine or feces of an infected multimammate mouse and rat, that remain carriers for life. Once infected, people may transmit Lassa virus in both community and health care settings, by contaminated medical equipment and direct contact with bodily secretions. About 15–20% of hospitalized people with Lassa fever will die from the illness. However, many infected people do not develop symptoms, which typically include fever, headache, vomiting and muscles pain. The main feature of fatal illness is impaired or severely delayed cell mediated immunity leading to fulminant viremia. Early recognition and initiation of targeted care increase patients surviving rates. Lassa fever is diagnosed by ELISA, which may detect IgM and IgG antibodies as well as Lassa virus antigen and RT-PCR used in the early stage of disease. There is currently no licensed vaccine against Lassa fever, and the only treatment available is based on ribavirin. In this article epidemiological aspects as well as diagnostics approaches are presented and discussed in the context of possibly increasing the public health threat with Lassa fever in European countries