The brand - targeted at "fashion forward twenty somethings" - saw total sales rise by 47% to £208 million in its final quarter to the end of August.
It said the number of active customers had grown to 7.1 million customers, up from 5 million at the same time last year.
Chief executive Nick Robertson said it was "strong finish to the financial year", with annual sales up 40% to £754 million.
"We expect profit before tax for the year to be marginally above expectations," he added.
The buoyant performance increases the likelihood of top managers at the firm including Mr Robertson sharing in a lucrative bonus pot of up to £30 million, which is dependent on them meeting a set of tough sales targets by 2015.
UK retail sales for the latest quarter were up 49% to £74 million, while international revenues leapt 47% higher to £134 million, including a 73% increase in the European Union.
ASOS, which stands for "As Seen on Screen", was founded in 2000 to target fashion-conscious young people by trying to emulate the styles of their favourite celebrities.
It is targeting £1 billion in sales by 2015.
Earlier this year, it announced a tie-up with Primark, allowing the budget fashion chain to sell clothes on the internet for the first time.
ASOS was hit by a high-profile departure during the summer when the influential former Marks and Spencer executive Kate Bostock walked out of a high-profile role after just six months saying the online retailer "isn't the right place for me".