Since 1998 collapse of tomato plants has been producing significant losses in protected tomato crops along the Spanish Mediterranean coast. Affected plants show sudden and progressive wilt followed by total collapse and death. Analysis of the distribution and accumulation of Pepino mosaic virus (PepMV) in collapsed and non-collapsed plants and the presence of the virus in all analysed collapsed plants suggests a relationship of this Potexvirus with tomato collapse. The fact that collapse does not occur on PepMV-free farms reinforces this hypothesis. PepMV-infected plants showed a necrotic area in the vascular system, mainly in the basal area of the stem. This necrosis was more pronounced in collapsed plants and in the areas with higher viral concentration. Our hypothesis is that tomato collapse would be associated with necrosis of the vascular system caused by PepMV accumulation.