Does a DVT in the leg always cause swelling? Or is it possible to have no noticeable swelling, just mild pain?

Dvt. Usually swelling occurs but not always If you have continued pain suggest a venous Doppler sonograms.
DVT/leg swelling. A leg DVT does not always cause leg swelling. The bigger the vein that has a clot the more the chance of swelling. In general, iliac, femoral or popliteal vein clots will cause swelling. Swelling is not common with clots in the veins below the knee (soleus, gastrocnemius, and tibial veins). The way to make the diagnosis is with a venous duplex ultrasound.