Joe Jonas checked into an emergency room in L.A. while doctors inspected his abs -- for severe stomach pains -- 48 hours after Joe did some late night partying in Chicago.

A rep for Joe confirms he went to the emergency room at Children's Hospital L.A. on Sunday. We're told Joe was only at the hospital briefly ... and it's not clear what was wrong with him.

One potential hint -- on Friday night (into Saturday morning) Joe was out at a Chicago hot spot Board Room Nightclub (above) partying ... and performed the next night in Chi-Town.

Whatever the problem was ... Joe felt good enough to eat out -- we spotted him and his bro Nick leaving Katsuya last night. Sushi after stomach troubles? Risky, Joe.

Nick Jonas, 18, and his older girlfriend Delta Goodrem, 26, enjoyed an adult unchaperoned vacation in Mexico this weekend.

Hasta la vista purity ring.

Check out some beachin' celebrity doppelgangers -- and vote for which star you think owns the look!

Wearing a vinyl sauna sweat top, newly single Jonas Brother Joe Jonas worked on his fitness in L.A. on Monday.



He's a lean, mean, boy band machine.

The Jonas Brothers' show must go on ... but it will go on without a replacement for their special guest act Demi Lovato.



A source connected with the tour tells TMZ, "There are no plans to replace Demi for the remaining six days on the Jonas Brothers Live in Concert tour."

As TMZ first reported, Demi decided to leave the tour and seek help for "physical and emotional issues" at a treatment facility.

Evangelical Christian boy bander Nick Jonas hugged it out with controversial marriage equality opponent and Saddleback Church pastor Rick Warren at Anaheim Stadium on Easter Sunday.



Jesus loves your skinny jeans.

Joe Jonas got his buff on by practicing his acrobatic skills on the beach in Santa Monica this weekend.



Purity rings aren't the only ones the 20-year-old can rock.

After finally confirming they are a couple, Demi Lovato and Joe Jonas stepped out in public yesterday to do a little platonic shopping in Los Feliz.



Rumors that they're the same size are not true.

Selena Gomez went shopping in Texas for her "boyfriend" on Tuesday -- and she got the perfect thing for him to play with in his pocket: A watch.



TMZ has learned the teen Disney idol was on the hunt for the perfect timepiece for a special friend -- if you believe the rumors, that friend is Nick Jonas. She picked it up at a jewelry store in the Northpark Mall in Dallas.

We're told she got the watch engraved with the phrase "Check the time ... I love you right now" -- and then personalized the box with a line from a Roy Croft love poem: "I love you, not only for what you are, but for what I am with you."

Good deal ... considering the total bill was only $148.31.

Former non-lovers Selena Gomez and Nick Jonas got cozy on a park bench by Lake Michigan in Chicago this weekend.


So much for Nick's solo career.

Happy honeymoon pal.