Aesthetic values are a key driver of tourist and recreational visitation to natural areas and are listed among the selection criteria for World Heritage properties. However, assessment and monitoring of aesthetic values in natural areas, and coral reefs in particular, have proven to be challenging. In our study we explored the value and limitations of a rapid assessment approach involving non-expert ratings of aesthetic beauty as a potential tool for long-term monitoring of aesthetic values in the Great Barrier Reef World Heritage Area, Australia. We investigated the sensitivity of a rating scale for detecting change and sampling requirements for monitoring, as well as observer biases, using an online survey of 1417 Australians in which respondents rated the aesthetic beauty of 181 coral reef images on a ten-point scale. Our results show average aesthetic rating scores ranged from 4.35 to 8.34 on a scale from 1 (ugly) to 10 (beautiful), with potential to detect differences of statistical significance within one point, indicating sufficient sensitivity to change for monitoring purposes. We found that a sample size of c.100 ratings per image provided a reasonable balance between cost (i.e. sample size) and accuracy (i.e. error). Older respondents (>65 years) with higher levels of coral reef visitation, experience and interest were more likely to give extreme ratings, however, there was no apparent predictor for this bias to be positive or negative (high or low ratings). Based on these results we provide recommendations to assist coral reef managers in their use and interpretation of non-expert aesthetic ratings in coral reef monitoring.