Leukemia is actually a group of different cancers of the blood cells. Leukemias can be acute or chronic, and people with chronic leukemias may not notice any symptoms before the condition is diagnosed with a blood test. Acute leukemias are more likely to cause symptoms. Symptoms of all forms of leukemia are related to the proliferation of abnormal blood cells and replacement of the bone marrow by the cancerous cells.

Symptoms of leukemia include fevers, night sweats, and swollen lymph nodes that are typically not painful or tender. Fatigue, weight loss, and bone or joint pain are other potential symptoms. Easy bruising and bleeding tendencies may result in bleeding from the gums, purplish patches on the skin, or small red spots under the skin.

Sometimes, there is swelling of the spleen or liver, causing pain or swelling in the abdomen. Frequent infections are another common sign of leukemia. If the brain is affected, there may be nausea and vomiting, confusion, headaches, seizures, or problems with muscle control.

Source: http://www.rxlist.com