The post-thrombotic syndrome (PTS) is a common, debilitating complication following deep venous thrombosis. PTS is a syndrome for which it has been difficult to provide a clear definition. PTS was defined as chronic venous signs/symptoms after a deep venous thrombosis. A number of scales are available to diagnose PTS, but there is a strong need for standardization. The Villalta scale was chosen as the standardized PTS scale. The Villalta scale has been validated in several studies and shows good correlation with generic and disease-specific quality of life scales. The inter-observer rate between study nurses and physicians was shown to be very good. Furthermore, the scale shows good discriminative properties among the different severity groups of PTS. The Villalta scale is useful for use in randomized controlled trials and it allows pooling of data from different studies. The Villalta scale should undergo further validation on intra-rater reliability. Ongoing randomized controlled trials will further validate the Villalta scale for use in PTS.