Net income edged lower to $16.4 million (£8.3m) in Q1, from $17.5m (£8.87m) in the first quarter of 2007.
Earl Hesterberg, Group 1 chief executive, said: "Although the new vehicle sales environment continued to be challenging during the first quarter, much of that profit pressure was offset by improvements in other areas of our business.
“The results this quarter continue to demonstrate the strength of our business model, with both the parts and service business and the finance and insurance business showing growth in this slowing new vehicle sales environment."
Group 1 entered the UK market after acquiring Chandlers BMW/Mini in March 2007. The group wants to push its portfolio up to 50 dealers throughout the UK.