Factor X (FX) deficiency is an autosomal recessive trait that occurs in fewer than 1 in 500 000 people. Not surprisingly, reports of prophylactic treatment for FX deficiency are exceedingly rare. We now report our experience of the use of prophylactic therapy in a FX-deficient patient. This 18-year-old African-American male presented at the age of 4(1/2) years with an FX level < 1%. Treatment was on demand with prothrombin complex concentrates (PCCs) given at two times the dose per kilogram of body weight for factor IX. He experienced frequent epistaxis, soft tissue bleeding and joint bleeding. The development of a target joint (right ankle) prompted the initiation of prophylactic treatment in the beginning of 1998 to the present with 30 units kg(-1) Profilnine twice per week via a home infusion programme. If breakthrough bleeding occurred, he was instructed to infuse another dose. He was instructed that Profilnine should not be infused in more than two doses in 24 h or on more than three consecutive days. A trough level drawn 48 h post-infusion showed an FX level of 30%. In the initial 12 months with prophylactic treatment, there was no breakthrough bleeding. Subsequently, with an additional 11 months of follow-up, he has reported one bleed. He rates his quality of life improved since starting prophylactic treatment. There have been no thrombotic events. Prophylaxis with PCC for FX deficiency with adequate education and follow-up can be performed capably in the home setting with a resultant decrease in the frequency of bleeding and attendant complications.