Abstract: Let Γ be a finitely presentable pro-p group with a nontrivial finitely generated closed normal subgroup N of infinite index. Then def(Γ) ≤ 1, and if def(Γ)=1 then Γ is a pro-p duality group of dimension 2, N is a free pro-p group and Γ/N is virtually free. In particular, if the centre of Γ is nontrivial and def(Γ) ≥ 1, then def(Γ)=1, cd G ≤ 2 and Γ is virtually a direct product F × Zp, with F a finitely generated free pro-p group. |