Online diamond retailer Blue Nile posted first quarter net sales of $74.1 million, an 18.7 percent year-over-year increase in sales and the highest first quarter sales level in the company’s history. Net income rose 23.1 percent to $2.4 million compared to $1.9 million in the first quarter of 2009.

Gross profit totaled $15.8 million. As a percentage of sales, gross profit improved 10 basis points to 21.3 percent. Operating income for the quarter grew 23.3 percent to $3.6 million, while Operating margin inched up 10 basis points to 4.8 percent of net sales.

“We are pleased with our first quarter results, including excellent growth in sales and earnings,” said CEO Diane Irvine. According to Irvine, the results reflect the strong fundamentals of Blue Nile’s business model. “Customers,” she added, “seek (…) tremendous value and an exceptional shopping experience.”

International sales grew 71.4 percent in the quarter to $9.6 million, again, a record first quarter increase for the company. Excluding the impact from changes in foreign exchange rates, international sales increased 51.8 percent.