© 2018 The Author(s) 2018. Background: Isavuconazole was compared to caspofungin followed by oral voriconazole in a Phase 3, randomized, double-blind, multinational clinical trial for the primary treatment of patients with candidemia or invasive candidiasis. Methods: Adult patients were randomized 1:1 to isavuconazole (200 mg intravenous [IV] three-times-daily [TID] for 2 days, followed by 200 mg IV once-daily [OD]) or caspofungin (70 mg IV OD on day 1, followed by 50 mg IV OD [70 mg in patients > 80 kg]) for a maximum of 56 days. After day 10, patients could switch to oral isavuconazole (isavuconazole arm) or voriconazole (caspofungin arm). Primary efficacy endpoint was successful overall response at the end of IV therapy (EOIVT) in patients with proven infections who received ≥1 dose of study drug (modified-intent-to-treat [mITT] population). The pre-specified noninferiority margin was 15%. Secondary outcomes in the mITT population were successful overall response at 2 weeks after the end of treatment, all-cause mortality at days 14 and 56, and safety. Results: Of 450 patients randomized, 400 comprised the mITT population. Baseline characteristics were balanced between groups. Successful overall response at EOIVT was observed in 60.3% of patients in the isavuconazole arm and 71.1% in the caspofungin arm (adjusted difference -10.8, 95% confidence interval -19.9 - 1.8). The secondary endpoints, all-cause mortality, and safety were similar between arms. Median time to clearance of the bloodstream was comparable between groups. Conclusions: This study did not demonstrate non-inferiority of isavuconazole to caspofungin for primary treatment of invasive candidiasis. Secondary endpoints were similar between both groups. Clinical Trials Registration: NCT00413218.