The objective of the study was to test the hypothesis that gender can be preselected by timing coitus in relation to ovulation, the marker of ovulation being the Peak symptom according to the Billings Method. A blind prospective study of 99 couples wishing to preselect the sex of their child was conducted in Nigeria, using the Post-Peak approach of Billings Method for males and Pre-Peak for females. Research co-ordinators examined the ‘post-conception’ form within four months of conception. This form recorded the timing of coitus prior to conception, and from this, the sex of child was predicted. 94 of the couples had a child of pre-selected sex showing a method success of 94.9%.