It is well-known that candidates listed first on the ballot paper tend to receive more votes than other candidates. However, experimental studies that confirm this truism mostly stem from first-past-the-post systems. Do we also find ballot position effects in PR systems where voters may vote for a party instead of a specific candidate? We investigate a natural experiment in Danish national elections involving more than 9,000 candidates on almost 100 different ballot papers. Our findings show that ballot positions, indeed, have a causal effect on election results in PR systems. Since Danish national elections constitute a least-likely case, our findings indicate that ballot position effects are much more empirically relevant than suggested by existing research.