The so-called “surf diatoms” constitute a small group of species that are present with great abundance in the surf zones of some sandy beaches where often the accumulations are dominated only for one of these species. They adhere to air bubbles generated by wave action forming green or brown patches that float in the surf zone, remaining as long streaks on the beach. In May 2015 a green accumulation was detected in Coquimbo Bay in northern Chile. The study of samples with light and electron microscopy techniques showed the presence of Aulacodiscus kittonii, a well-known surf diatom. This is the first report of this kind for Chile and for the whole coast of the Eastern South Pacific Ocean with A. kittonii as the dominant species. It is also the first report for Chile as a living taxon. A description of the Chilean specimens is given with comments and photographs on the variation of some of its morphological features.