A cross-sectional study was performed to assess the correlation between telephone and self-administration of patient-related outcomes (PROs) used in the assessment of ankylosing spondylitis (AS) patients. Participants underwent a telephone interview in which the following measures were evaluated: numerical rating scales (NRSs) for global health, pain intensity, global pain, back pain, and back pain at night; BASDI, BASFI, Health Assessment Questionnaire (HAQ), ASQoL, EuroQol, SF-12, and Work Productivity and Activity Impairment (WPAI) questionnaire. Within 48 h after the telephone interview, patients were appointed for a clinical visit in which the same questionnaires and in the same order were self-administered. The degree of correlation of outcomes measures between telephone interview and self-administration was assessed with the intraclass correlation coefficient (ICC). The two modes of assessing PROs were highly reliable, with ICC of 0.81 for BASDAI, 0.82 for BASFI, and 0.75 for HAQ. NRSs for global health, global pain intensity, back pain, and back pain at night also showed ICCs between 0.51 and 0.70, and only NRS for global disease activity showed an ICC of 0.45. This results were similar in patients with AS and patients with psoriatic arthritis. Social functioning and mental health domains of the SF-12 as well as EuroQol had poor correlations. The ICCs for WPAI outcomes were very good or good. We conclude that PROs in AS patients are comparable in both self-administered paper questionnaires and via a telephone interview. Different modes of assessing PRO measures facilitate the assessment of patients with AS in routine practice.