We show that under some conditions, imposed on coatoms and maximal idempotents of a pseudo BL-algebra, we can decompose a pseudo BL-algebra M as an ordinal sum and we show that then M is linearly ordered. We investigate pseudo BL-algebras with a unique coatom a and with a maximal idem-potent, and analyze two main situations: either a(n) - a(n+1) holds for some n >= 1, or a(n) > a(n+1) hold for any n >= 1. We note that there exist (subdirectly irreducible) algebras with two coatoms that are not linearly ordered, so the restriction to a single coatom is natural. (C) 2011 Mathematical Institute Slovak Academy of Sciences