A transition from La Niña to ENSO-neutral conditions occurred during May 2011 as indicated by generally small sea surface temperature (SST) anomalies across the equatorial Pacific Ocean. The latest weekly Niño index values showed near-average SSTs in the central and east-central equatorial Pacific. Notice the figure below the absence of the "below average" sea surface temperatures that would typically be associated with the La Nina regime.
The duration of this La Nina was just less than 12 months, which is on the low end of the "average" duration of a La Nina event.
CLICK HERE for a full discussion on the end to La Nina.