BACKGROUND Regular factor XIII (FXIII) prophylaxis is standard treatment for congenital FXIII A-subunit deficiency (FXIII-A CD). Recombinant factor XIII-A2 (rFXIII-A2) was extensively evaluated in the mentor trials. OBJECTIVE To assess real-world safety and treatment effectiveness of rFXIII-A2 prophylaxis from the mentor 6 trial. METHODS mentor 6 was a noninterventional, postauthorization safety study investigating rFXIII-A2 prophylaxis in FXIII-A CD. rFXIII-A2 treatment was observed for 2 to 6 years per patient. The primary end point was documentation of adverse drug reactions (including anti-FXIII antibody development). Secondary end points were serious adverse events (SAEs), medical events of special interest (MESIs), and annualized bleeding rate (ABR). RESULTS Among 30 patients (mean age, 25.5 years), there were 44 adverse events (AEs) (30 mild, 13 moderate, 1 severe). Eleven AEs were possibly/probably related to rFXIII-A2. Of four MESIs, two were unlikely related to rFXIII-A2 (accidental overdose, deep vein thrombosis), and two were possibly/probably related (nonneutralizing anti-FXIII antibody, decreased therapeutic response). All 10 SAEs were unlikely related to rFXIII-A2. Over a follow-up of 75.4 patient-years, there were six treatment-requiring bleeds (all trauma-related with no spontaneous bleeds), giving a treatment-requiring ABR of 0.066; five bleeds were treated successfully with rFXIII-A2. Eight of nine minor surgeries performed during rFXIII-A2 prophylaxis reported successful hemostatic outcomes (one missing evaluation). CONCLUSIONS These data confirm that rFXIII-A2 prophylaxis is well tolerated as long-term care. There were no spontaneous bleeds, ABR was low, and rFXIII-A2 successfully treated bleeds in patients receiving rFXIII-A2 prophylaxis.