Endometriosis is a chronic gynaecological condition, of which pain is both the most common and most debilitating symptom. As with other forms of pain, there is increasing recognition of the role of psychological processes in bridging the gap between pain and pain impact, and yet these processes are not well understood in endometriosis. The aim of this study was to investigate the relevance of fear of progression, imagery, and interpretation bias in endometriosis, and their contribution to pain interference. A total of 221 participants (mean age = 38 years, SD = 7.8) with endometriosis were recruited from Endometriosis Australia. This cross-sectional study included relevant demographics and endometriosis characteristics; questionnaires to measure fear of progression, imagery, interpretation bias, and pain; and the word association task to measure interpretation bias. Participants reported high scores on the Fear of Progression Questionnaire (M = 38/60), higher than that has been found in cancer. Controlling for age and pain intensity, we found that imagery, interpretation bias, and their interaction were associated with increased fear of progression and that fear of progression was associated with greater pain-related interference. In exploratory analysis, we also found that the frequency and distress of endometriosis-related intrusive imagery were associated with greater fear of progression and pain interference, after controlling for age and pain intensity. These findings provide the first support of the importance of fear of progression in people with endometriosis and suggest possible pathways for causal investigation.