To investigate the silent circulation and transmission of arthropod-borne viruses (arboviruses) in the Fako Division of Cameroon.This survey was conducted based on clinical observations and laboratory diagnosis; field collections of mosquitoes.This study was conducted in the Fako Division of South West Cameroon.One hundred and two sera were obtained from febrile patients (with negative laboratory findings for malaria and typhoid fever) at clinics in the Fako Division, and diurnal anthropophilic mosquitoes (4,764) collected.Virus isolation was attempted from these, and sera were screened for antibodies against 18 African arboviruses by haemagglutination inhibition (HI) and complement fixation (CF) tests.No virus was isolated. Fifty three of 79 (67.1%) sera reacted with one or more viral antigens. Twenty nine sera (36.7%) reacted with members of the genus Alphavirus, with Chikungunya (CHIKV) and O'nyong-nyong (ONNV) viruses as the most frequent (34.2%). Forty six sera (58.2%) reacted with members of the genus Flavivirus: 24 (30.4%) were cross-reactive, but 11.4% reacted monotypically with Zika, 5.1% with yellow fever virus (YFV), 5.1% with dengue virus-2 (DENV-2), 2.5% with DENV-1 and 1.3% with Wesselsbron virus, respectively. The plaque reduction neutralisation test used to specify the agent that elicited the response could not resolve 33.3% of the cross reactions between CHIKV and ONNV. Neutralising antibody titres against ONNV and CHIKV were very high indicating probable re-infection.Our results indicate previously undetected circulation of arboviruses in Cameroon, and suggest that they are important, overlooked public health problems.