3 months duration because of its relatively rapidity of actiont its capacity to effect sustained improvement with ongoing therapy and the higher level of patient retention on therapy""Methotrexate is a folate antagonist, it causes reduction in cells reproductive abilities. Methotrexate affects cells, which divides quickly. In psoriasis cells divide more than usual. Methotrexate binds to these cells and inhibits enzymes involved in rapid growth of skin cells. It is commonly used to stop the progression ofpsoriatic arthritis and less commonly used in the treatment of severe psoriasis with no arthritis component Methotrexate is an effective antipsoriasis agent. It is especially useful in acute generalized pustular psoriasis, psoriatic erythroderma, psoriatic arthritis and extensive chronic plaque psoriasis.Methotrexate although widely used has not been shown benefit in ankylosing spondylitis. There is not enough evidence to be certain of the benefit and harms of methotrexatefor ankylosing spondylitis amhnore research is needed. In ankylosing spondylitis the use of methotrexate is not recommended for the axial manifestations. The drug may have some efficacy- in the peripheral involvement. For this disease there is lack of clinical trials and most of the trials did not show efficacy on the axial symptoms of the disease.">