A European coronary angioscopy working group has been established to create and evaluate a classification system for angioscopic observation. The 'Ermenonville' classification features items, graded in 3-5 categories, such as lumen diameter, shape of narrowing, colours of surface, atheroma, dissection, thrombus, etc. Inter- and intra-observer agreement on the interpretation of angioscopic images, using this classification system, was studied within the working group. Kappa values for chance-corrected intra-observer agreement of the diagnostic items were 0.51-0.67. The mean kappa values for inter-observer agreement were very low at 0.13-0.29. The important items, such as red thrombus and dissection were studied after recoding as either present or absent. These items proved to have a good intra-observer agreement, and an acceptable inter-observer agreement after recoding. Other angioscopic diagnoses should be made with caution. Multicentre angioscopy studies should make use of an angioscopy core laboratory. A set of definitions for coronary angioscopy is proposed, and this working group will re-evaluate observer agreements using these definitions.