There are many ways in expressing relative frequencies with numerical values: 1) percentages 25%, 2) decimal fractions 0.25, 3) common fractions 1/4, 4) natural frequencies “1 out of 4”, 5) notations like “every fourth”, or 6) odds “1 to 3”. The latter one plays an important role in communicating changes of risk, e.g., in medical research results in scientific papers. Therefore, we investigate medical students’ and—as a comparison group—also law students’ abilities in converting different representations of relative frequencies into odds. 52 medical students and 51 law students answered three items, which addressed the conversion of a relative frequency into odds. The low solution rates indicate that odds ratios are probably poorly understood because the underlying concept—namely the odds themselves—are frequently misinterpreted. These findings support previous claims for not reporting odds ratios in scientific papers, because these can be misunderstood.