7059 Background: Recent years have seen the introduction of TT for pts with AML and HR- MDS (> 10% marrow blasts). New criteria, less stringent than those for CR, for response to these agents have been promulgated, giving rise to the response category HI. However, the effect of achieving HI on survival is uncertain. Methods: 180 pts, median age 73, with AML or HR-MDS received TT, most commonly decitabine (69 pts), from 2000–2006. Treatment-related death occurred in 11%, CR in 28%, CRp in 6%, and 55% (99 pts) were resistant. We examined survival in these 99 according to whether TT produced HI, blood count criteria for which were as defined by the International Working Group (IWG) for MDS. Initially, we, unlike the IWG, did not require any duration of HI, however; in subsequent analyses, we required durations of = 4 weeks (HI-4) and, like the IWG, = 8 weeks (HI-8). Results: Survival time dated from start of TT was similar in the 32 pts who achieved HI and the 67 who did not. However, the 13 pts with HI-8 lived longer than those with shorter or no HI (48% vs. 11% at 2 years, p=0.01) as did the 14 with HI-4 (p=0.01). Because HI-4 and HI-8 pts had to live long enough to achieve and maintain HI, we re-did the analysis including only the 84 pts who lived = 67 days from start of TT, the median time needed to observe HI-4. This analysis, which included HI-4, age, and cytogenetics as predictors of survival, indicated that HI-4 was the strongest predictor of longer survival (HR 0.34, 95% CI 0.13–0.86, p=0.02). Results were analogous when we limited the analysis to the 68 pts who lived at least 138 days, by which time 75% of HI-4 pts had achieved HI (p=0.06). Conclusions: Our results suggest that HI-4 (or HI-8 as defined by the IWG) following TT confers a survival benefit in AML or HR-MDS. No significant financial relationships to disclose.