The most common defensive vocalization in anurans is the distress call. However, few descriptions of this type of call are available in the literature, especially for the Neotropics. We therefore described the defensive calls of 31 anuran species and evaluated correlations between anuran size and call physical structure (sound pressure level, dominant frequency, and call duration). Defensive calls are most likely an ancestral character in anurans, as this character is widespread over several genera and families. A positive relationship may exist between the physical characteristics of distress calls and chances of avoiding predation, i.e., only larger (than a certain size) frogs produce defensive vocalizations and the larger the frog, the higher the sound pressure level of its screams. This study strengthens our knowledge about defensive vocalizations in anurans and will hopefully instigate new challenges for future research.