Background: Platelet transfusions are frequently used in the intensive care unit (ICU), but current practices including used product types, volumes, doses and effects are unknown. Study design and methods: Sub-study of the inception cohort study ‘Thrombocytopenia and Platelet Transfusions in the ICU (PLOT-ICU)’, including acutely admitted, adult ICU patients with thrombocytopenia (platelet count <150 × 10⁹/L). The primary outcome was the number of patients receiving platelet transfusion in ICU by product type. Secondary outcomes included platelet transfusion details, platelet increments, bleeding, other transfusions and mortality. Results: Amongst 504 patients with thrombocytopenia from 43 hospitals in 10 countries in Europe and the United States, 20.8% received 565 platelet transfusions; 61.0% received pooled products, 21.9% received apheresis products and 17.1% received both with a median of 2 (interquartile range 1–4) days from admission to first transfusion. The median volume per transfusion was 253 mL (180–308 mL) and pooled products accounted for 59.1% of transfusions, however, this varied across countries. Most centres (73.8%) used fixed dosing (medians ranging from 2.0 to 3.5 × 10¹¹ platelets/transfusion) whilst some (mainly in France) used weight-based dosing (ranging from 0.5 to 0.7 × 10¹¹ platelets per 10 kg body weight). The median platelet count increment for a single prophylactic platelet transfusion was 2 (−1 to 8) × 10⁹/L. Outcomes of patients with thrombocytopenia who did and did not receive platelet transfusions varied. Conclusions: Among acutely admitted, adult ICU patients with thrombocytopenia, 20.8% received platelet transfusions in ICU of whom most received pooled products, but considerable variation was observed in product type, volumes and doses across countries. Prophylactic platelet transfusions were associated with limited increases in platelet counts.