While the photochemistry of duplex DNA has been extensively studied, the photochemistry of nonduplex DNA structures is largely unexplored. Because the structure and stereochemistry of DNA photoproducts depend on the secondary structure and conformation of the DNA precursor, they can serve as intrinsic probes of DNA structure. This review focuses on the structures and stereoisomers of pyrimidine dimer photoproducts arising from adjacent and nonadjacent pyrimidines in A, B and denatured DNA, bulge loops, G‐quadruplexes and reverse Hoogsteen hairpins and methods for their detection. While irradiation of duplex DNA produces adjacent cis,syn cyclobutane pyrimidine dimers (CPDs), irradiation of other structures can produce other isomers, such as the nonadjacent trans,anti CPD formed in G‐quadruplexes. This review investigates the various types of adjacent and nonadjacent dipyrimidine photoproducts and methods for their detection that could be used to identify the presence of various types of unusual structures in DNA.