This case study examined the translation performance of four professional translators with the aim of exploring the cognitive effort involved in direct and inverse translation. Four professional translators translated two comparable texts from English into Spanish and from Spanish into English. Eye-tracking technology was used to analyze the total time spent in each task, fixation time, and average fixation time. Fixation count in three areas of interest was measured including: source text, target text, and browser, used as an external support. Results suggested that although total time and fixation count were indicators of cognitive effort during the tasks, fixation count in the areas of interest data showed that more effort was directed toward the source text in both tasks. Overall, this study demonstrates that while more traditional measures for translation difficulty (e.g., total time) indicate more effort in the inverse translation task, eye-tracking data indicate that differences in the effort applied in both directions must be carefully analyzed, mostly regarding the areas of interest.