Background As part of the strategies the Bioko Island Malaria Control Project has implemented in recent years, around 80 000 insecticide treated nets (ITN) were delivered to the population in 2007. This study assesses the determinants of bed net usage and bed net ownership in children under 5.

Methods Data were selected from 2008 and 2009 annual surveys of households who had at least one child under 5. Outcome variables were: sleeping under a net/ITN the night prior to the survey and household ownership of at least one net. The explanatory variables were household characteristics and caregiver's knowledge of malaria.

Results A total of 3210 households with 5151 children under 5 were analysed. Higher bed net usage was associated with being sick in the last 14 days prior to the survey, urban area, more years of education of head of households, household ownership of at least one ITN and the year 2009. The proportion of households that owned at least one net in 2009 declined by 32% when compared to 2008. Knowing how malaria is prevented and transmitted, having fewer children under 5 and having more children sick in the previous 14 days were associated with higher household net ownership.

Conclusions The fall in bed net usage from 2008 to 2009 is attributable to the striking decline in ownership. Although ownership is similar in rural and urban areas, rural households are less likely to protect their children with nets. Knowledge about malaria seems an important determinant of bed net ownership.