Published research on the effects of fungal interaction on disease development and subsequent mycotoxin accumulation was reviewed, focusing on pathogens related to Fusarium Head Blight (FHB). Almost all published studies showed that competitive interactions are the rule when fungal/disease development is considered. The fungi with the competitive advantage did not usually colonise significantly more than when inoculated alone, i.e. there was no advantage gained by the dominant pathogen from the presence of other weaker competing fungi. However, the effects of fungal interactions on mycotoxin accumulation were generally more complicated. Total mycotoxin production in mixed inoculation may decrease, increase or remain at a similar level compared with single-isolate inoculation, depending on the fungal species concerned and environmental conditions. However, the lack of accurate quantification of each competing fungal component in mixed inoculations in many studies prevented an accurate estimation of mycotoxin productivity per unit fungal biomass. A few recent studies, where each individual fungal component was quantified using molecular methods, suggested that mycotoxin productivity in mixed inoculations generally increased.