This report from Brazil describes two cases of likely ZIKV transmission by blood transfusion from one presymptomatic infected person who donated platelets by apheresis on January 16, 2016. The two leukodepleted platelet units were irradiated with 25 Gy delivered by an IBL-437C gamma irradiator (Cis Bio International) and were transfused in different patients on January 19 (day 0). On January 21, the donor called the blood bank to report a cutaneous rash, retro-orbital pain, and pain in both knees that had begun on January 18. An investigation was initiated under the hospital’s clinical protocol for transfusion-associated adverse events, with the donor and both patients providing written informed consent.