Cinnamyl alcohol dehydrogenase (CAD, E.C. 188.8.131.52) is a monolignol biosynthetic enzyme that catalyzes the final step of lignin subunit biosynthesis in higher plants. Recently, a mutant allele of the cad gene, cad-n1, encoding for the CAD enzyme, was discovered in loblolly pine. By reducing the expression of the cad gene, this mutant has a decreased lignin content and major changes in the lignin composition in wood. In this study, we found that the substitution of a wild-type allele by cad-n1 was associated with a significant effect on 2nd-year shoot elongation in a half-sib family of loblolly pine (designated family 7-1037). The average effect of cad-n1 appeared to increase with tree growth and was greater for stem radial growth than height growth. An increase of 14.1% in de-barked volume in year 4 was associated with cad-n1. Co-segregation analysis indicated that the cad locus itself might represent a gene that governs stem growth in pine. The significance of the mutation cad-n1 for tree growth and wood processing is discussed.