Lymphedema occurs when your lymph vessels are unable to adequately drain lymph fluid – usually from an arm or leg. Lymphedema can be either primary or secondary. This means it can occur on its own (primary lymphedema) or it can be caused by another disease or condition (secondary lymphedema). Primary lymphedema is a rare, inherited condition caused by problems with the development of lymph vessels in your body. It occurs most frequently in women.