This paper examines the Discussions of Spanish medical research articles and Spanish translations of comparable English-language texts in order to determine how far their discourse and theme–rheme patterns differ. Quantitative analysis revealed two discourse patterns. Spanish authors preferred a progressive style characterized by considerable initial background information, and a commentary opening with a statement of result and ending with the main claim. In contrast, most translations exhibited a retrogressive style with little or no background information, and the main claim located early or at the start. The Spanish texts showed a highly cohesive thematic pattern, most within-paragraph links being with the immediately preceding theme or rheme, whereas the translations, influenced by the source texts, contained comparatively more distant links, thus creating thematic ‘jumps’. Thematic progression was independent of discourse pattern. Qualitative analysis identified a number of strategies that can help translators align their texts with the target language norm for theme–rheme progression.