Felid herpesvirus-1 (FeHV-1) and feline calicivirus (FCV) are the most important infectious causes of respiratory disease in cats. FeHV-1 and FCV co-infections are common in cats with upper respiratory tract disease, but it is unknown whether such co-infections also occur in cats with pneumonia. This study examined the lungs of naturally infected cats with FeHV-1 pneumonia for FCV co-infection by histopathology and immunohistochemistry. The frequency of FCV (13/21, 62%) in this group of cats suggests that co-infection is common in kittens with FeHV-1 pneumonia. FCV infected macrophages were often found in the lumen of FeHV-1 affected airways. In 8/13 (62%) cats, typical FCV lesions were distant from changes induced by FeHV-1. FCV infection of type II pneumocytes/alveolar macrophages was apparent in histologically unaltered areas. It is likely that damage to airways induced by FeHV-1 facilitates secondary infection with FCV due to reduced mucociliary clearance and impaired immune defences.