Androgenetic alopecia (AGA), is the most common form of hair loss both in men and women , it is caused by transformation of the terminal hair in to vellus hair. Homocysteine is a sulfhydryl containing non-protein coding amino acid formed mainly as a byproduct in the methionine metabolism.Compare homocysteine level in patients with and without androgenetic alopecia and evaluate the relation between homocysteine and BMI and smoking in both studied groups.60 patients with androgenetic alopecia and 20 age and sex matched healthy volunteerssubjected to age, sex, body mass index (BMI), smoking history ,laboratory investigation for measurement of the serum level of homocystiene. serum homocystiene level was found to be increased in androgenetic alopecia patients combared to controls. Homocystiene showed a significant (p < 0.05)  positive correlation with BMI and smoking.This prospective study showed that there were association between elevated homocystiene level ,smoking,BMI, and severity of androgenetic alopecia in addition to serum level of homocystiene can be used as an early prediction for AGA diagnosis.