Total retail sales rose to £605.7m from £444.3m the year before, while total group revenue was up 36% to £621.3m.
In the UK, retail sales were up 18% to £244m, while US retail sales increased 66% to £82.7m.
Sales in the EU were 49% higher at £165.8m, while Rest of World sales rose 46% to £113.2m and international sales grew 52% to £361.7m.
International sales were helped by the reinvestment of the FX tailwind resulting from the pound's weakness in the aftermath of the Brexit vote and US import duty benefits.
Active customer numbers were up 25% in the period and the average basket value rose 2%, while total orders shipped increased 35% on the year to 15.5m.
ASOS maintained its medium-term reported sales growth guidance at between 20% and 25% per annum, but upped its guidance for full-year reported sales growth to between 25% and 30% from a previous range of 20% to 25% following reinvestment of FX and U.S. duty benefits.
CEO Nick Beighton said: "Following record sales over Cyber weekend and the Christmas trading period, I'm pleased to report a strong start to the year. A 50% plus increase in international sales is a standout performance. UK sales growth at 18% was a strong performance in a more promotional market.
"With sales for the year now expected to be up by about 25 to 30%, we're accelerating our infrastructure investment to handle that growth. ASOS remains well set to meet its longer-term ambitions as a result of the hard work and commitment of the team."
Numis, which rates the stock at 'buy', said the update was "very strong", with retail sales growth of 36% comfortably ahead of consensus expectations of 29%.
"We retain our positive stance, confident that ASOS' unique proposition will support sustainable long term growth as a global fashion destination."
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