Prestressed and nailed laminated timber bridge decks are made from laminates which, because of their being usually shorter in length than the deck span, are butt-jointed at regular intervals. In calculating deflections of such decks, it is usual to ignore the reduction in flexural rigidity of the deck caused by the presence of the butt joint. The effect of butt joints on the flexural rigidity of the laminated deck is studied analytically, and it is shown that the deflections of a deck having such joints may be significantly larger than those of a deck without them. A simple method is presented to account conservatively for the presence of butt joints in the calculation of the deflections of a prestressed laminated timber deck.Key words: timber bridge, laminated deck, butt joint, prestressed wood deck.