Patient/caregiver out-of pocket costs associated with hematopoietic cell transplantation (HCT) are not well known. We conducted a pilot study to evaluate patient/caregiver out-of-pocket costs in the first 3 months after allogeneic HCT. Thirty patients were enrolled at three sites. Before HCT, participants completed a baseline survey regarding household income and insurance coverage. Subsequently, they maintained a paper-based diary to track daily out-of-pocket expenses for the first 3 months after HCT. Telephone interviews were conducted to follow-up on the missing/incomplete diaries and on study completion. Twenty-five patients/caregivers completed the baseline survey. Among these, the median pre-tax household income was $66 500 (range, $30-$375 000) and 48% had to temporarily relocate close to the transplant center. Insurance coverage was managed care plan (56%), Medicaid (20%), Medicare (17%) and other (8%). Twenty-two patients/caregivers completed 4 diaries; the median out-of-pocket expenses were $2440 (range, $199-$13 769). Patients/caregivers who required temporary lodging had higher out-of-pocket expenses compared with those who did not (median, $5247 vs $716). Patients/caregivers can incur substantial out-of-pocket costs over the first 3 months, especially if they need to temporarily relocate close to the transplant center. Our study lays the foundation for future research on the early and long-term financial impact of allogeneic HCT on patients/caregivers.