The Barrens darter Etheostoma (Catonotus) forbesi (Teleostei: Percidae) is a rare stream fish endemic to the upper Caney Fork River system in the Barrens Plateau region of middle Tennessee. We studied the darter's population characteristics and selected aspects of its nesting biology at 10 sites surveyed during April 2004. In our survey, we caught a total of 75 Barrens darters at a rate of 21 individuals per hour of backpack-electrofishing effort. At least one male Barrens darter was present at six of the 10 sites. Females outnumbered males by a ratio of 1.4 to 1. Total lengths ranged 44–97 mm, averaging 62 mm for females and 78 mm for males. The number of Barrens darters seen in the present survey was similar to a 1994 survey. However, both surveys reveal a species in need of conservation, with low abundance at most known sites within its limited geographic range. We found 20 Barrens darter nests located on the flat undersides of cobbles with a mean length, width and thickness of 17 × 13 × 5 cm. Nests in one stream, Duke Creek, were located at a mean water depth of 22 cm, column current velocity of 15 cm/s and bottom velocity of 7 cm/s. Stream channel widths averaged 3.5 m at nest rock locations. Nests contained a mean number of 463 eggs (range 69–976) arranged in a monolayer. Male size and the number of eggs per nest were positively correlated with nest rock size for eight nests where we captured the attending guardian male; however, egg number was not correlated with rock size for all nests in the study.