The occurrence and distribution of wetwood in balsam fir (Abies balsamea (L.) Mill. was investigated from the standpoint of determining the factors affecting its formation. Young, rapidly growing trees, namely those with wide annual rings, were found to be most subject to wetwood. This has been attributed to an incomplete branch healing, which promotes the direct entry of rainwater to the stem. Branch healing associated with narrow annual rings was such that it prevented water penetration. Wetwood in balsam fir was concentrated in the mid-stem region, becoming progressively less prevalent in the branchless lower bole and towards the living crown. The internal distribution of wetwood is explained by the prevalence of branch stubs in the region of the mid-stem and the capacity of such branches to trap and conduct water to the interior.