In four flocks, 215 dairy ewes were monthly sampled, throughout lactation, in order to study the relationship between subclinical intramammary infections (IMI) and milk individual SCC (iSCC). A decision rule proposes to consider an udder as healthy (specificity = 75%) if every iSCC are lower than 0.500×106 cells/ml and infected (sensitivity = 82%) if at least two iSCC are higher than 1 or 1.2 million cells/ml. At a flock level (annual geometric mean of bulk SCC), this rule allows the estimation of the prevalence of subclinical IMI: an annual bulk SCC of 0.650×106 cells/ml corresponds to a prevalence of 15%. These results are discussed.