This brief is an update of a 2017 analysis examining the characteristics of ACA marketplace rating regions with one or two participating insurers. We found that the number of markets with one or two marketplace insurers has decreased between 2018 and 2019, meaning markets have become more competitive this year. However, they have not yet regained the level of competition they had in 2017. In regions with one insurer, the median benchmark premium (for the second lowest cost silver plan) for a 40-year-old nonsmoker is $592 per month in 2019 compared with $376 in rating regions with 5 or more insurers. We also found that, in recent years, premium growth has been higher in rating regions with one insurer than in those with 5 or more insurers.