In this paper the role of language competence and thematic competence in translation and post-editing was studied. The sample included 49 translation students who translated part of a copyright agreement from English into Hungarian under two different conditions, from-scratch human translation and post-editing. Our findings indicated that there was no difference between from-scratch human translation and post-editing in terms of quality and speed, and that time spent on task was only loosely connected to achievement. We also found that thematic (legal) knowledge, as assessed by our multiple-choice test, did not correlate with from-scratch human translation/post-editing performance. Perhaps the most important finding of the study is that source language (SL) reading plays a key role in translation students' performance, whether it is traditional from-scratch human translation or post-editing. It was also highlighted that SL reading was even more important in post-editing than in from-scratch human translation, and that weaknesses in reading competence may lead to different types of errors in the two working conditions.