Onychophagia is defined as chronic nail biting behaviour, which usually starts during childhood. Onychotillomania results from recurrent picking and manicuring of the fingernails and/or toenails, leading to visual shortening and/or estraction of nails. The aim of this study was to assess the prevalence of onychophagia and onychotillomania in young adults, and the comorbidity of these conditions with anxiety disorders and obsessive compulsive disorders (OCD), as well as to determine factors related to these behaviours. A total of 339 individuals were interviewed with a structured questionnaire. Onychophagia was present in 46.9% of participants (including 19.2% active and 27.7% past nail biters), and an additional 3 people (0.9%) had onychotillomania. The majority of subjects (92.2%) described nail biting as an automatic behaviour. Tension before nail biting was reported by 65.7% of nail biters, and feelings of pleasure after nail biting by 42%. Among the participants with lifetime onychophagia, 22.5% met criteria of anxiety disorder and 3.1% of OCD, while in the group without onychophagia at least one anxiety disorder was diagnosed in 26.2% and OCD in 5.0%. We did not find any correlation between nail biting and other anxiety disorders or OCD. In conclusion, no single condition was associated with nail biting or influenced such behaviour; multiple psychological factors were involved.