Background: In the randomized phase III DASISION trial of dasatinib v IM in newly diagnosed CML-CP, dasatinib showed higher and faster rates of complete cytogenetic response (CCyR) and major molecular response (MMR) (Shah Blood 2010 116 abs 206). Methods: Pts received dasatinib 100 mg once daily (QD) (n=259) or IM 400 mg QD (n=260). Primary endpoint was confirmed CCyR (cCCyR; CCyR on 2 consecutive tests) by 12 mos. Results: After 19.7 mos’ median follow-up (range 0.1–31.4), 81% and 80% remained on dasatinib and IM. 18-mo response rates for dasatinib v IM were: cCCyR 78% v 70%, P=0.0366; CCyR 84% v 78%, P=0.0932; and MMR 56% v 37%, P<0.0001. MMR occurred more often with dasatinib in all Hasford groups. For dasatinib v IM, 13% v 7% had a BCR-ABL level ≤0.0032%. In time to response analyses, dasatinib pts were 1.8-/1.5-fold more likely to have MMR/CCyR (both P<0.0001). For dasatinib v IM, 6 (2.3%) v 9 (3.5%) pts transformed to accelerated/blast phase (AP/BP) on study; 1 other pt transformed 183 days after discontinuing dasatinib. For dasatinib v IM, 18-mo rates (follow-up ongoing) were overall survival: 96% v 98%; progression-free survival (no AP/BP or loss of response): 95% v 94%; failure-free survival (ELN 2006 criteria): 93% v 90%; and maximum clinical benefit (no progression, failure or intolerance): 87% v 86%. Drug-related adverse events (AEs) are shown (Table). Grade 3/4 nonhematologic AE rates were ≤1%. Pleural effusions seen only with dasatinib (2% gr 1, 9% gr 2, <1% gr 3) did not seem to impact efficacy. Most cytopenias (75%) arose within 4 mos. Gr 3/4 lab abnormality rates were ≤3% except hypophosphatemia (dasatinib 5%, IM 24%). For dasatinib v IM, 56% v 39% had dose interruption, 25% v 14% had dose reduction and 6% v 4% discontinued due to drug-related AEs. Minimum 24-mo follow-up will be presented. Conclusions: At 18 mos, dasatinib continues to show superior efficacy over IM and acceptable tolerability, supporting first-line dasatinib use in newly diagnosed CML-CP.