Twelve colonies where the Red-legged Cormorant (Phalacrocorax gaimardi) breeds in Argentina were visited. Physical and biological characteristics were recorded at 29 nesting cliffs and at different sectors within cliffs. Forty-five percent of the cliffs were located on continental shores, the rest were on islands. Cliff height and length varied (mean height = 14 ± 5 m, length range = 12 to 3,000 m) but their slope was commonly 80 to 90°. Most cliffs had more than 50% of the total available area with apparent suitable breeding sites. Cliff length and available area was positively correlated with the number of nests. Forty-nine different sectors used by Red-legged Cormorant on the cliffs were identified. In those sectors, number of active nests was positively correlated and nest density negatively correlated with area. Highest median density of nests was NE in orientation, protected from predominant winds. Minimum average distance from the tide line to the closest nest group was positively correlated with both wave effect exposure (fetch in front of the sector) and cliff slope. Probability of occurrence of active Red-legged Cormorant nests in a sector increased with cliff slope. Forty-one percent of cliffs also had nests of the Rock Shag (Phalacrocorax magellanicus). For Red-legged Cormorant, cliff slope, orientation, available area and exposure to waves seemed important for nesting.