Clomiphene citrate is the drug most commonly prescribed for ovulation induction. It is the first choice medication in normogonadotrophic oligo/amenorrhoeic infertility (WHO group 2), essentially associated with polycystic ovaries. Anovulatory women who are responsive to clomiphene citrate should be treated for at least six cycles and the treatment should probably be limited to a maximum of 12 cycles. It is necessary to monitor at least the first cycle with ultrasonography because of the risk of multiple pregnancy and the variable response of patients to different doses of clomiphene. In addition, the risk of ovarian hyperstimulation syndrome should not be underestimated. More triplets and higher order pregnancies result from ovulation induction than from in vitro fertilization, and multiple pregnancy has many risks for both mother and babies. The role of empirical clomiphene in the treatment of unexplained infertility is debatable and the present data are inconclusive. Obesity, hyperandrogenaemia and insulin resistance are important factors in clomiphene-resistant patients. Failure to ovulate in response to clomiphene has been approached by either medical or surgical treatment. An effective alternative medical treatment is gonadotrophin injections. Treatment with metformin and the new generation of insulin-sensitizing drugs is under evaluation. The most widely used surgical treatment today is laparoscopic ovarian drilling, which appears to be as effective as gonadotrophin therapy.