Background: Tenofovir disoproxil fumarate (TDF) as first-line therapy for chronic HBV infection is related to nephrotoxicity. Tenofovir alafenamide fumarate (TAF) has been approved with a similar virological and serological response, but lower toxicity. TAF is available for older patients, with bone or kidney impairment. Methods: The primary objective was the evaluation of renal function modification in patients who are switching from TDF to TAF; secondary objective was the use of urinary concentration of tenofovir (TFV) as early marker of renal function improvement or worsening.Retrospective study including all HBV patients treated with TDF or TAF. Two groups were selected: patients who are switched from TDF to TAF and who continued with TDF. Follow-up was six months. Results: 42 subjects were included; 17 were in TAF group (40 %) and 25 in TDF group (60 %). In TDF group, no estimated glomerular filtration rate (eGFR) improvement was observed, while in TAF group increased by 9 ml/min (p