Malaria is one of the most important parasitic diseases in the world. It is caused by parasites of the genus Plasmodium sp., which enter humans through the bite of mosquitoes of the genus Anopheles. Automated hematology analyzers based on flow cytometry have been widely used to aid in the diagnosis of malaria, based on the existence of alterations in the scatter plots that suggest the presence of parasites of the genus Plasmodium. The case of a 55-year-old male patient is presented, worker from a Costa Rican rural zone, correlating the alterations in channel DIFF and WBC/BASO of the Sysmex XT-1800i® hematological analyzer with what was found in the thick drop. The objective of this case report is to demonstrate the utility of hematological analyzers in the detection of relapses, reinfections and follow-up in patients diagnosed with malaria.