Early diagnosis and treatment of malaria (EDTM) is a key component of malaria control. The success of EDTM depends on health seeking behaviour and the quality of the health service. This study assessed self-diagnosis, treatment and treatment delay after the introduction of EDTM in 1993. In southern Vietnam EDTM comprises microscopic diagnosis and free treatment with artemisinin derivatives at public health facilities. Until 2001, 1698 questionnaires had been completed by patients participating in randomized treatment trials of uncomplicated malaria. The presumptive self diagnosis 'malaria' increased from 68% in 1993 to 100% in 2001 and self-treatment decreased, from 74% to 8% in 2000 and 24% in 2001. The median (maximum) delay between first symptoms and seeking treatment at a public health facility decreased from 3 (23) to 1.3 (3) days (P<0.001) Concomitant was a significant decline of reported incidence of malaria-associated mortality, severe malaria and uncomplicated malaria. If offered an attractive package of EDTM, patients become sensitized to the possibility of malaria and less likely to self-treat. EDTM should be provided as soon as possible to all symptomatic patients, aiming at reducing treatment delay to a maximum of 2 days.