In the condition of deep vein thrombosis, blood clots occur in the deep veins, that is, the veins not on the surface of the skin. Deep vein thrombosis can develop in any part of the body. However, in most cases, it is seen that deep vein thrombosis occurs in the legs or the pelvic region. This happens probably because the lower body experiences more pressure than the upper part of the body. Deep vein thrombosis is a rather serious condition and, if left untreated, can give rise to serious complications.