Differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS) and Raman spectroscopy have revealed a complex melting/crystallization behaviour of poly(N-methyldodecano-12-lactam), MPA. After cooling from the melt to crystallization temperature T-c of 250-280 K, primary lamellar structure is formed which melts at about 324 K. During later stages of isothermal crystallization, imperfect "fringed" crystallites melting at about T-c + 10 K are formed in the interlamellar space of the primary structure. On heating, additional crystallization of the primary lamellae takes place with an optimum temperature at about 300 K. In the case of isothermal crystallization at T-c = 290 K and higher, the two steps of the primary structure formation combine in a single isothermal step. Under certain conditions an additional endotherm, possibly corresponding to some less-defected "fringed" lamellae, was detected. On further heating, the primary crystallites undergo recrystallization with an optimum temperature at about 327 K. The final higher-ordered structure melts at about 335 K. Melting temperature of the imperfect crystallites shows a strong dependence while that of the highest-melting structure a negligible dependence on T-c. Within 24 h at 300 K, the MPA sample reaches crystallinity of about 34%.