The diagnosis or early detection of lymphedema is difficult. The first signs may be subjective observations such as “my arm feels heavy” or “I have difficulty these days getting rings on and off my fingers”. These may be symptomatic of early stage of lymphoedema where accumulation of lymph is mild and not detectable by any difference in arm volume or circumference (see severity above). As lymphedema develops further then definitive diagnosis is commonly based upon an objective measurement of difference between the affected or at-risk limb at the opposite unaffected limb, e.g. in volume or circumference.

Symptoms may include severe fatigue, a heavy swollen limb or localized fluid accumulation in other body areas, including the head or neck, discoloration of the skin overlying the lymphedema, and eventually deformity (elephantiasis).

Lymphedema should not be confused with edema arising from venous insufficiency, which is not lymphedema. However, untreated venous insufficiency can progress into a combined venous/lymphatic disorder which is treated the same way as lymphedema.