Human polyomaviruses such as JC polyomavirus and BK polyomavirus have long been well known pathogens of immunocompromised patients. Several new members of this viral family have been described during the last decade. Human polyomavirus 9 seems to be a novel pathogen of transplanted patients according to some studies. The aim of our study was to determine the presence of human polyomavirus 9 in patients after kidney or stem cell transplantation (SCT) at the University Hospital in Hradec Kralove, Czech Republic. Overall 100 patients, 65 after kidney transplantation and 35 after SCT, were included into the study. At least three follow-up samples from each patient were examined for human polyomavirus 9 DNA presentation with the two previously described in-house PCR protocols. Despite the frequent reactivation of human CMV (14.3% in kidney transplantation and 63.3% after SCT) or BK polyomavirus in our patient group, there was no positivity for human polyomavirus 9 either in blood samples or urine samples. One of the possible reasons for this discrepancy versus previous published studies could be a relatively low proportion of patients treated by induction therapy before kidney transplantation in our study cohort.,? 2017 Wiley Periodicals, Inc.