Dash 8-200
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Flight Crew Overcame Equipment Problem; Flight Crew Returned To Clearance
Aircraft
All operations prior to climb were normal.  ATC assigned an altitude of 11;000 feet.  11;000 feet was set in the altitude selector.  The autopilot was engaged in the following modes: LNAV; ALT SEL and in pitch (pitch attitude was set at 5 degrees nose up).  These parameters were verified and confirmed.  As the aircraft approached 11;000 feet the aircraft pitched up to more than 10 degrees nose high and did not capture the 11;000 foot assigned altitude.  Both the FO and myself noticed this happen at the same time and also noticed 8000 fpm where 'pitch' was indicated prior.  I immediately disconnected the autopilot and began a descent back to 11;000 feet.  The highest altitude we saw on the altimeter was 11;400 feet.  I directed the FO to contact ATC and inform them what happened.  ATC acknowledged and proceeded as normal.  We continued that flight and reengaged the autopilot with no other abnormal operations.
[Report narrative contained no additional information].
Dash 8-200 flight crew reported an altitude overshoot resulted when the autopilot pitched up for unknown reasons.