Dilated cardiomyopathy (DCM) is a major cause of morbidity and mortality in various dog breeds. The diagnosis of overt DCM is not normally problematic, although the importance of active exclusion of other causes of the dilated, hypokinetic heart is emphasised. Recent interest in human familial DCM has prompted a number of researchers to investigate the genetic basis of canine DCM. Prospective screening of dogs from lines with familial prevalence of DCM may identify dogs with pre-clinical ("occult") DCM. Dogs with other echocardiographic abnormalities or arrhythmias may also be identified. It is clear that dogs, like humans, have a prolonged pre-symptomatic phase of the disease extending over years. The ESVC DCM taskforce was established to provide the veterinary cardiology community with guidelines for the diagnosis of DCM, predominantly based on 2D and M-mode echocardiography. Diagnosis of DCM requires all of the following: (i) Left ventricular dilatation (ii) Reduced systolic function (iii) Increased sphericity of the left ventricle. We propose a scoring system for the identification of dogs in the pre-clinical stages. These include a number of major criteria and minor criteria. Future prospective longitudinal studies are required to test these in different breed populations to assess their predictive power and further refinements may be required. The importance of post mortem confirmation of disease is emphasised, and the two major histopathological features associated with DCM, the attenuated wavy fibre and the fibro-fatty infiltration-degenerative forms, require further investigation to identify the different aetiopathogenetic factors which may be involved.