Narrative:

After boarding was complete ATC notified us of a 50 minute gate hold. I made appropriate periodic pas to passengers. Our wheels up was :50 so I told agent and crew to plan to push at :40. At push time no one was ready. I had to go to the top of the jet way to find the agent and there was no pushback crew. As a result we were rushed despite the 50 minute delay. At this point there was a serious chance that we would not make our wheels up time. At the last moment the a flight attendant tossed the napkin on to the console and closed the cockpit door. The last digit of the count was illegible and I made the mistake of assuming it was correct. As we approached the runway we were cleared for immediate takeoff. I rang the cabin to notify the flight attendants and as we took the runway the a called up to tell us that there was a passenger that thought he might be on the wrong aircraft. I had the first officer instruct everyone to remain seated and that we would sort it out in the air. Above 10;000 feet I confirmed the load sheet count of 46 and compared it to the napkin count of 4 (illegible). I contacted the a who said her count was 47. Further investigation revealed that our extra passenger was a connect for [a different airport] that had failed to exit at the last stop and remained on the aircraft despite the numerous pas referring to our destination. I suspect that he was in the lav during the through count process. We coordinated with dispatch to have a [customer service agent] meet him.slow down; it's always wise to slow down. Also; our procedure of verifying the count as the very last thing to occur before push; seems like there could be a better time to discover this showstopper; especially when faced with a potentially significant delay if an error is detected. Maybe I haven't been paying attention but I ride other airlines and I've never seen flight attendants actually count passengers before pushback. The potential error chain has too many links with our system.

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Original NASA ASRS Text

Title: B737NG flight crew reported they departed with an unaccounted passenger onboard.

Narrative: After boarding was complete ATC notified us of a 50 minute gate hold. I made appropriate periodic PAs to Passengers. Our wheels up was :50 so I told Agent and Crew to plan to push at :40. At push time no one was ready. I had to go to the top of the jet way to find the Agent and there was no Pushback Crew. As a result we were rushed despite the 50 minute delay. At this point there was a serious chance that we would not make our wheels up time. At the last moment the A Flight Attendant tossed the napkin on to the console and closed the cockpit door. The last digit of the count was illegible and I made the mistake of assuming it was correct. As we approached the runway we were cleared for immediate takeoff. I rang the cabin to notify the Flight Attendants and as we took the runway the A called up to tell us that there was a Passenger that thought he might be on the wrong aircraft. I had the First Officer instruct everyone to remain seated and that we would sort it out in the air. Above 10;000 feet I confirmed the load sheet count of 46 and compared it to the napkin count of 4 (illegible). I contacted the A who said her count was 47. Further investigation revealed that our extra Passenger was a connect for [a different airport] that had failed to exit at the last stop and remained on the aircraft despite the numerous PAs referring to our destination. I suspect that he was in the lav during the through count process. We coordinated with Dispatch to have a [customer service agent] meet him.Slow down; it's always wise to slow down. Also; our procedure of verifying the count as the very last thing to occur before push; seems like there could be a better time to discover this showstopper; especially when faced with a potentially significant delay if an error is detected. Maybe I haven't been paying attention but I ride other airlines and I've never seen flight attendants actually count Passengers before pushback. The potential error chain has too many links with our system.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.