Voice comparison in forensic phonetic casework requires the assessment of the similarity of the target voices. This task may be impeded by the speakers’ attempt to disguise their voice. The objective of this study is to map the strategies of voice disguise as employed by 100 native speakers of Common Czech. In agreement with findings in other languages, changes in speaking fundamental frequency appeared in most speakers, and phonatory modifications were the second most frequent type of disguise. Other strategies included modifications of the resonance characteristics of the voice, melodic and temporal changes. Recognition difficulty and naturalness of the disguise were also assessed. In addition, several acoustic parameters in the natural and disguised condition were compared in 15 speakers whose disguise rendered recognition more difficult.