Lianas can have a large impact on the diversity structure and dynamics of tropical forests yet they remain essentially unknown even in some of the most intensely studied tropical forests such as La Selva Biological Station in Costa Rica. We quantified the diversity abundance and mortality of lianas in primary and selectively logged forest at La Selva for over 3 years from January 1999 until July 2002. We measured identified permanently marked and mapped all lianas >=1.3 m in length and 2 mm in diameter whether climbing or free-standing in nine 24 m x 36 m (864 m2) plots. There were no significant differences in density diversity or mortality between primary forest and areas that were selectively logged approximately 50 years prior to our study. We found a mean density of 1493 lianas ha-1 and a mean species richness of 23 species per 864 m2 plot. Annual mortality was 9.4% over all size-classes but was the highest for the smallest individuals (=5 cm) was much lower over the 3.5-year period (3.2% per year) and the five most abundant species suffered no mortality in this size-class. In contrast to many lowland neotropical forests where Bignoniaceae and Fabaceae are reported to be the dominant liana families at La Selva we found that Sapindaceae was the most speciose family and Dilleniaceae the most abundant. Moutabea aculeata (Polygalaceae) was the most abundant species constituting approximately 17% of the individuals and having the lowest mortality of all 60 species. The 10 most abundant species at La Selva accounted for more than 60% of all individuals. Compared to other lowland sites in the neotropics including other wet forests the abundance and diversity of lianas at La Selva are very low.