Having noted a lack of oral corpora of Spanish twins’ voices, we have collected a database which consists of the following malespeakers: 24 monozygotic twins, 10 dizygotic twins, 8 non-twin brothers, and 12 non-twin reference-population speakers. Twenty-two voice-related studies about twins have been reviewed in order to account for the average sample size of previous twin corpora, as well as their data collection method. Within a forensic-phonetic approach, the study of twins’ voices is particularly relevant, as these (especially monozygotic twins) represent the most extreme physical similarity in human beings. Distinguishing them is therefore a challenge in speaker identification.