Narrative:

The captain was flying, I was working the radios. We were sbound at 9000 ft MSL (going into ord). The controller told us to descend and maintain 7000 ft. I read back 7000 ft air carrier X. I put 7000 ft in radio altimeter and the captain confirmed it. After reaching 7000 ft, the controller said air carrier X please confirm altitude. I said 7000 ft. He said 'I must have read it wrong I wanted you at 8000 ft.' we asked if there was any traffic problems or if he wanted us to climb to 8000 ft. He said no just maintain heading and altitude. I did read back 7000 ft over the radio but was not corrected at that time so we went to 7000 ft. To our knowledge there was no conflict because of our altitude.

Related reports:

Google
 

Original NASA ASRS Text

Title: A COMMUTER FO ALLEGES THAT ORD APCH CTLR ISSUED A DSCNT TO 7000 FT WHEN THE CTLR ACTUALLY MEANT DSND TO 8000 FT. NO OTHER TFC INVOLVED.

Narrative: THE CAPT WAS FLYING, I WAS WORKING THE RADIOS. WE WERE SBOUND AT 9000 FT MSL (GOING INTO ORD). THE CTLR TOLD US TO DSND AND MAINTAIN 7000 FT. I READ BACK 7000 FT ACR X. I PUT 7000 FT IN RADIO ALTIMETER AND THE CAPT CONFIRMED IT. AFTER REACHING 7000 FT, THE CTLR SAID ACR X PLEASE CONFIRM ALT. I SAID 7000 FT. HE SAID 'I MUST HAVE READ IT WRONG I WANTED YOU AT 8000 FT.' WE ASKED IF THERE WAS ANY TFC PROBS OR IF HE WANTED US TO CLB TO 8000 FT. HE SAID NO JUST MAINTAIN HEADING AND ALT. I DID READ BACK 7000 FT OVER THE RADIO BUT WAS NOT CORRECTED AT THAT TIME SO WE WENT TO 7000 FT. TO OUR KNOWLEDGE THERE WAS NO CONFLICT BECAUSE OF OUR ALT.

Data retrieved from NASA's ASRS site as of July 2007 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.