December marks the second consecutive month that Lillard has earned the rookie honor.
Lillard averaged 18.2 points and 6.9 assists to lead all rookies while helping Portland to a 9-4 record in December. With Lillard leading the point, Portland is now 16-14 on the season and in eighth place in the Western Conference standings.
Lillard is averaging 18.4 points and 6.3 assists per game for the season, and joins Brandon Roy as the only other Trail Blazer in history to earn multiple rookie of the month honors. Roy earned the honors in three consecutive months, January to March, in 2007.
Lillard was selected sixth overall by the Blazers in the 2012 NBA Draft and has appeared in all 30 games for the team this season.