The method of treating varicose veins and other vascular diseases provides sclerosant fluid through a catheter into the body vessel to be treated. The catheter has a lumen and a plurality of sidewall exits. The sclerosant fluid is provided under sufficient pressure so that it comes out of each exit as a jet of fluid with sufficient velocity to impinge on the vessel wall substantially orthogonal to the wall and thus minimize dilution of the sclerosant fluid and optimize coverage. A movable sheath on the catheter permits selecting a portion of the exits to be uncovered and thus create an infusion zone for the jets of sclerosant fluid which approximately match a desired treatment zone.