LOS ANGELES — Disney reported mixed quarterly results on Tuesday, with per-share profit declining by 17 percent and revenue climbing by 36 percent. Costs associated with building its Disney Plus streaming service occupied much of the gap.

But investors and Disney’s Hollywood competitors were interested in only one number: Disney Plus subscribers. There were 28.6 million as of Monday, the company said, an astounding number for a service that is less than three months old. Robert A. Iger, Disney’s chief executive, told analysts on a conference call that the response to Disney Plus had “exceeded even our greatest expectations.”

Disney unveiled its flagship streaming platform on Nov. 12 amid a thundering marketing campaign and found immediate success with “The Mandalorian,” a live-action “Star Wars” series that introduced a blockbuster character known as Baby Yoda. Within a day of its introduction, Disney Plus had 10 million subscribers, including an unspecified number of accounts for customers who signed up free under a promotion with Verizon, blowing past analysts’ estimates. Disney Plus costs $7 a month for those paying the sticker price.

Average monthly revenue per paid subscriber in the quarter was $5.56. Mr. Iger said popular offerings included the 2016 musical “Moana” and old episodes of “Hannah Montana” and “The Simpsons.” And, of course, “The Mandalorian,” which Mr. Iger said would return for a second season in October.