Narrative:

Departed normally. At cruise; approximately 25 mins into the flight; the first officer reported feeling ill. I (the captain) told him to try breathing some oxygen from the cockpit mask. Within mins; he reported feeling worse; and asked me to land the aircraft as soon as possible. I contacted center; declared an emergency; and requested vectors to the nearest field. We requested medical personnel meet us at the gate. We landed at ZZZ on runway without incident.

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Original NASA ASRS Text

Title: AN ACR FO BECAME ILL DURING FLT. CAPT DIVERTED TO A NEARBY ARPT TO GET FO MEDICAL AIDE.

Narrative: DEPARTED NORMALLY. AT CRUISE; APPROX 25 MINS INTO THE FLT; THE FO RPTED FEELING ILL. I (THE CAPT) TOLD HIM TO TRY BREATHING SOME OXYGEN FROM THE COCKPIT MASK. WITHIN MINS; HE RPTED FEELING WORSE; AND ASKED ME TO LAND THE ACFT ASAP. I CONTACTED CTR; DECLARED AN EMER; AND REQUESTED VECTORS TO THE NEAREST FIELD. WE REQUESTED MEDICAL PERSONNEL MEET US AT THE GATE. WE LANDED AT ZZZ ON RWY WITHOUT INCIDENT.

Data retrieved from NASA's ASRS site as of January 2009 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.