Scanning tunneling microscopy is used to study the surface structural and electronic properties of cleaved single crystals of Bi2.15Sr1.7CaCu2O8+ Images with atomic resolution reveal atomic chains with sinusoidal modulations running along the perovskite cell axis with a periodicity of 9 to 10 unit cells. These atomic chains stack along the b direction with a translational vector of one unit, resulting in an incommensurate periodicity of about 4.75 units along the a direction. In contrast to other reports, no evidence of missing Bi-atom rows is found. Spectroscopic studies show zero density of states at the Fermi level, implying that the surface Bi-O layer is nonmetallic. © 1989 The American Physical Society.