Booking Holdings (NASDAQ:BKNG) has been one of the most successful companies of the past 15 years, clawing its way back from a near-death experience in the aftermath of the dot-com bust. Amazing long-term growth has fueled its share-price gains, and the company has continually managed to prove naysayers wrong about the sustainability of its business model. Yet as Booking Holdings has gotten larger, it's been more difficult to sustain the growth that investors have come to take for granted.

Coming into Thursday's first-quarter financial report, Booking Holdings investors were actually prepared to see almost no revenue growth and a decline on the company's bottom line. Even though the online travel provider's results couldn't even live up to those relatively low expectations, shareholders seemed to take heart at the idea that Booking Holdings might recover heading into the much busier summer travel season.

Booking Holdings logo and subdomains.

Image source: Booking Holdings.

An ugly start to 2019

Booking Holdings' first-quarter results left a lot to be desired on their face. Revenue for the quarter was down 3%, to $2.84 billion, which was quite a bit worse than the $2.93 billion in sales that most of those following the stock were expecting. Adjusted net income declined even more sharply, falling 14%, to $508 million. That produced adjusted earnings of $11.17 per share, missing the consensus forecast among investors for $11.26 per share on the bottom line and just barely managing to fall within Booking Holdings' own guidance range for the period.

Slowdowns showed up in other areas of Booking Holdings' business. Gross travel bookings were up just 2%, to $25.4 billion, although the strong U.S. dollar cost the company about 6 percentage points of growth on that front. Agency revenue fell 8% from year-ago levels, and it took a nice 15% rise in merchant revenue to offset most of the downward pressure on the agency side. Advertising and other revenue was down about 1% over the period.

Deterioration in Booking Holdings' key product lines continued. Room-night counts were up just 10%, to 217 million, slowing even further from recent quarters. Rental-car days fell 1.3%, to 18 million. The only bright spot was a 4.4% rise in airline tickets booked under the platform.

CEO Glenn Fogel kept his comments terse. "Q1 was a solid start to the year," Fogel said, and the CEO pointed to the room-night growth as the highlight of the period.

Can Booking Holdings get its growth mojo back?

Booking Holdings also tried to stay upbeat about the future. In Fogel's words, "We continue to execute against a very large market opportunity and will manage our business with a long-term view in order to capture it."

Yet the guidance that the online travel specialist gave for the second quarter didn't exactly point to a huge acceleration in growth. The company projected hotel room-night booking growth of between 6% and 8%, the same as it projected last quarter, and total gross travel bookings will again end up between negative 1% to 1%. However, Booking Holdings now sees revenue growing 5% to 7% for the second quarter, even with 5 percentage points of currency-related pressure, and investors were pleased to see calls for adjusted net income of $965 million to $985 million, or between $22.15 and $22.60 on a per-share basis.

Booking Holdings shareholders responded well to the results, and the stock climbed 4% in after-hours trading following the announcement. However, in order to justify investors' optimism, Booking Holdings will have to deliver much better results than its guidance suggests. If that doesn't happen, then it could spell the end of Booking Holdings' impressive growth run -- and potentially hurt its future returns, as well.