Lamdassem returned to the Edinburgh Cross Country in 2012 and won the long race, beating European champion Yeshetela. He won the European Club's Cross Country meet in Castellón, leading Bikila Toledo to the title. He debuted over the marathon distance at the Lake Biwa Marathon but finished 23rd with a relatively slow time of 2:14:39 hours. Returning to shorter distances, he came second to Kenenisa Bekele at the Great Ireland Run and won the Cursa Bombers in April. In June he was a silver medallist at the European Cup 10000m and placed sixth in the event at the 2012 European Athletics Championships. He was selected to run the event for Spain at the 2012 London Olympics, but did not perform as well, coming in 23rd place in 28:49.85 minutes. In his first half marathon in eight years, he came seventh at the Great Scottish Run. A better outing came at the Great South Run 10-miler, where he was runner-up, and near the end of the year he came sixth at the 2012 European Cross Country Championships.