SummaryAcute cellular rejection (ACR) the first year after heart transplantation (HT) and its impact on survival was investigated. All 215 HT patients at our centre 1988-2010, including 219 HTs and 2990 first-year endomyocardial biopsies (EMBs), were studied. 'Routine' EMBs obtained 1,2,3,4,6,8,10,12,16,20,24,32, 40 and 52 weeks after HT, and 'additional clinically indicated' (ACI) EMBs, were graded according to the 1990-ISHLT-WF. The frequency and severity of first-year ACRs was low, with 6.5% of routine EMBs and 14.1% of ACI EMBs showing ACR ≥ grade 2. Proportionally more (P < 0.05) first-year ACRs ≥ grade 2 were found among EMBs in HTs performed during 1988-1999 (9.6%) than 2000-2010 (5.5%), EMBs performed during 16-52 weeks (8.8%) than 1-12 weeks (6.3%) after HT, EMBs in HTs with paediatric (11.3%) than adult (7.1%) donors, and EMBs in sex-mismatched (10.4%) than sex-matched (6.3%) HTs. Five-and ten-year survival was furthermore lower (P < 0.05) among HTs with ≥1 compared with 0 first-year ACRs ≥ grade 3A/ 3B (82% vs. 92% and 69% vs. 82%, respectively). Ten-year survival was 74% compared with 53% in the ISHLT registry. In conclusion, our results indicate that first-year ACRs ≥ grade 3A/3B affect long-term survival. We believe frequent first-year EMBs may allow early ACR detection and continuous immunosuppressive adjustments, preventing low-grade ACRs from progressing to ACRs ≥ grade 3A/3B, thereby improving survival.