Leukaemia comes in two forms acute and chronic.

• Acute means that the disease has a speedy onset and must be treated quickly.
• Chronic means that the disease has a slow onset and may run a prolonged course. The disease is divided into four main categories, which have different age and gender distribution.
• Acute myeloid leukaemia (AML) in younger people is equally common in either sex, but in the over 50's there is an increase in the proportion of males.
• Chronic myeloid leukaemia (CML) is very rare in younger people, but gets more common in old age.
  
• Acute lymphoblastic leukaemia (ALL) is very rare in older patients, but accounts for 85% of leukaemias in children.
• Chronic lymphocytic leukaemia (CLL) hardly ever occurs in childhood. CLL is most commonly found in people over 50 years of age.