A new and devastating physiological disorder of Vitis vinifera cv. Merlot was recently reported, known as premature berry dehydration (PBD), which is characterized by plant growth reduction, induction of general senescence and pedicel necrosis in the fruit, causing significant reductions in vineyard production. The causes of this disease remain unclear and previous reports suggest that it may be associated with phloem disruption and water provision. For this reason, any factor causing phloem disturbances could cause an important change in the berry water status. As some micro-organisms have been reported to disrupt phloem flow, we analyzed the occurrence of phytoplasma and viruses in commercial vineyards presenting PBD. In this study, a phytoplasma was detected by electron microscopy and nested PCR while virus infections were diagnosed by RT-PCR in samples collected during two growing seasons. The presence of phytoplasma only in samples from grape plants with PBD suggests that this pathogen may be one of the causal agents of this disorder. We suggest that the influence of other factors, such as virus infections, agronomic handling and environmental conditions also modulate berry dehydration. This is the first study at the microscopic and molecular levels that correlates phytoplasma presence with PBD.