Identification of quantitative trait loci (QTL) provides insight into the genetic control of growth and body composition in pigs. The majority of QTL have been identified on autosomes with less QTL reported on the sex chromosomes. A reason may be that the genomic analysis of the X chromosome is more statistically challenging. Computer programmes accounting for the unique features of chromosome X have been unavailable until recently. Most studies have adopted a regression-based approach analysing males and females separately, which results in a decrease in power to detect QTL. In the present study, a QTL analysis of pig chromosome X (SSCX) was carried out using a method which accounts for the unique features associated with chromosome X, including the pseudoautosomal region of the Y chromosome.