One of the main factors determining profitability of dairy farms is the reproductive efficiency of cows. Reproductive performance depends on many factors, being the existence of uterine pathologies one of the most relevant. Incidence of uterine diseases in dairy cattle is high and it is believed to be the cause of numerous reproductive failures. During the last years, researchers have shown great interest in subclinical endometritis because of the high incidence in the postpartum of dairy cows, and it has lead to the development of simple diagnosis methods. However, despite the high number of studies on subclinical endometritis published in the last years, many unknown aspects still exist. For example, there are different opinions concerning the best diagnosis method: endometrial cytology, uterine ultrasound or biopsy. In the case of cytology, the most used method, there is no unanimous opinion regarding the percentage of PMN that should be considered the cut-off point for diagnosing subclinical endometritis. Therefore, depending on the PMN cut off considered, the incidence of the process reported by the different authors may widely differ. On the other hand, effects of subclinical endometritis on reproduction may also differ in different studies, and it is still unclear how those effects are generated. In this review, main aspects on subclinical endometritis will be addressed.