In most developing countries, unmet need for family planning is a real problem among women in general, and adolescent girls in particular. The aim of this paper is to show that adolescent unmet need for family planning is more pronounced in some regions than in others, to identify the factors that accentuate this disparity, and to determine the sources of change in adolescent unmet need for family planning from 2004 to 2018 in Cameroon. To achieve these objectives, data from the 1998, 2004, 2011 and 2018 DHS were mobilized. At national level, the main source of variations in BNS_PF among adolescent girls in union is the behavior effect, and this is true for girls in the Grand Nord and Grand Ouest regions. It also appears that, region of residence is the primary explanatory factor for the occurrence of spaced SNBs among teenage girls in union.