OBJECTIVE To compare the cost effectiveness of recombinant human FSH (Gonal-F; Serono, Inc., Randolph, MA) and urinary FSH (Fertinex; Serono, Inc.) for ovarian stimulation during IVF with or without intracytoplasmic sperm injection for the treatment of infertility. DESIGN Clinical decision analysis techniques (the Markov model) were used to model the direct medical costs per patient during assisted reproductive technology. MAIN OUTCOME MEASURE(S) Clinical and economic outcomes of two different ovarian stimulation protocols (recombinant human FSH or urinary FSH) during three treatment cycles were considered. RESULT(S) More ongoing pregnancies were achieved, with fewer stimulation cycles, after recombinant human FSH (Gonal-F) than after urinary FSH (Fertinex) (40,665 versus 37,890). In addition, recombinant human FSH was also found to be more cost effective per ongoing pregnancy. From a societal perspective, the mean cost per pregnancy was $40,688 for recombinant human FSH versus $47,096 for urinary FSH. From the insurers' perspective, the mean cost/pregnancy for recombinant human FSH was $28,481 versus $32,967 for urinary FSH. CONCLUSION(S) Recombinant human FSH (Gonal-F) is not only more efficient clinically than urinary FSH (Fertinex), but also more cost effective. This analysis illustrates the point that the economic effectiveness of a drug depends less on its acquisition costs and rather more on the clinical outcomes associated with its use.