Background: Malaria disease causes enormous morbidity and mortality worldwide. More than 2 million people die annually; the majority of these children under the age of five living in Sub-Saharan Africa. Despite this high prevalence of disease, there is also a high degree of overdiagnosis and overtreatment.Objective: A clinical study in Tanzania, where the aim was to enhance the reliability of malaria diagnostics by assessment of the sensitivity and specificity of thrombocytopenia and raised lactate dehydrogenase (LDH) in malaria infected patients. Methods: 179 patients with malaria symptoms were included. Blood slide, full blood count (FBC), LDH, glucose and rapid tests (NOW and ASSURE) were performed. Results: Thrombocytopenia was significantly more frequent in the malaria positive group compared to the malaria negative. No such difference was found for LDH, most likely due to technical circumstances at the study site. In addition, there were a higher amount of anemic patients in the malaria positive group. There were few false negative blood slides. Out of the malaria positive 96% had infection with P.falciparum, and 4% had P.vivax, P.malaria or P.ovale.Discussion: FBC is not routinely performed in this particular hospital, but from our findings we believe that thrombocytes and hemoglobin (Hb) would be valuable tools in the diagnostic workup for suspected malaria. A great number of patients with negative blood slides were treated as if they had malaria, and other causes for their symptoms were often not pursued. As false negatives were seldom, a negative blood slide should initiate investigation for other diseases.