OBJECTIVES: To assess the degree to which variations in publicly reported hospital scores arising from the English Cancer Patient Experience Survey (CPES) are subject to chance. DESIGN: Secondary analysis of publically reported data. SETTING: English National Health Service hospitals. PARTICIPANTS: 72 756 patients who were recently treated for cancer in one of 146 hospitals and responded to the 2016 English CPES. MAIN OUTCOME MEASURES: Spearman-Brown reliability of hospital scores on 51 evaluative questions regarding cancer care. RESULTS: Hospitals varied in respondent sample size with a median hospital sample size of 419 responses (range 31-1972). There were some hospitals with generally highly reliable scores across most questions, whereas other hospitals had generally unreliable scores (the median reliability of question scores within individual hospitals varied between 0.11 and 0.86). Similarly, there were some questions with generally high reliability across most hospitals, whereas other questions had generally low reliability. Of the 7377 individual hospital scores publically reported (146 hospitals by 51 questions, minus 69 suppressed scores), only 34% reached a reliability of 0.7, the minimum generally considered to be useful. In order for 80% of the individual hospital scores to reach a reliability of 0.7, some hospitals would require a fourfold increase in number of respondents; although in a few other hospitals sample sizes could be reduced. CONCLUSIONS: The English Patient Experience Survey represents a globally unique source for understanding experience of a patient with cancer; but in its present form, it is not reliable for high stakes comparisons of the performance of different hospitals. Revised sampling strategies and survey questions could help increase the reliability of hospital scores, and thus make the survey fit for use in performance comparisons.