Background and objectives Chronic venous insufficiency of the lower limbs is characterized by symptoms and signs produced by venous hypertension due to structural and functional abnormalities of veins as a result of underlying reflux or obstruction that may eventually g ive rise to lower extremity edema ,pigmentation pain ,ulceration . The main objective is to study the spectrum of findings on colour duplex sonography in patients with clinical suspicion of CVI and to identify the patients who can be taken up for varicose surgery by locating and ruling out DVT in them.Methods :A prospective study was carried out in 50 patients with clinical suspicion of chronic venous insufficiency. All the clinically diagnosed patients with CVI referred to Rajah Muthiah Medical college & Hospital were subjected to colour flow duplex examination using (3-12 MHz) linear array transducer. Results : Of the total 50 cases, 42 cases showed positive doppler findings,8 cases were normal. Males predominated in our study (76%) and positive doppler findings were higher in them (78.57 %). Swelling (32%) and varicosities (24%) were the most predominant symptoms. Prolonged hospitalization was the most common predisposing factor in patients diagnosed to have DVT(27.8%) and occupational-prolonged standing ( 33.33%) factor were the commonest in patients with other causes of varicosities. The predominant involvement was unilateral (90.48 %) and left lower limb (61.9 %). GSV varicosity (75%) predominated in our study, with SFJ incompetence noted in 45%. Among the p ositive doppler cases (42),18 cases was diagnosed to have DVT. Thrombus was confined to femoro- popliteal segment in (83.33%) suggesting thrombus is more common in femoro- popliteal segment(proximal ) than than in distal segment. Severe form of CVI with ve nous ulcer were noted in 8 cases of which 7 case(87.5%) showed underlying DVT. Suggesting that underlying DVT with deep venous reflux is seen in most severe forms of CVI and thus it should be excluded in to provide a safe and effective treatment. Interpretation and conclusion It has been conclusively established that colour duplex sonography is safe, non invasive ,accurate,easily repeatable,widely available and cost effective in diagnosis of chronic venous insufficiency especially to exclude underlying DVT and thus helping in providing valuable information of therapeutic significance.