We examine the influence of the macromolecule chain length on the cloud point temperature (T cp ) and the temperature of the coil-to-globule transition (T M ) in aqueous solutions of hydrophobically modified (HM) telechelic poly(N-isopropylacrylamides) (PNIPAM) ranging in concentration from 0.01 to 35 g L -1 (0.1-310 mmol of NIPAM L -1 ). The telechelic HM-PNIPAM samples with n-octadecyl termini were obtained by RAFT polymerization of NIPAM in dioxane in the presence of S-1-n-octadecyl-S′-(R,R′-dimethyl-R′′-N-n-octadecylacetamide)trithiocarbonate as a chain transfer agent. Their molar mass (M n ) ranged from 12 000 to 49 000 g mol -1 with a polydispersity index lower than 1.20. The cloud point temperatures, measured by monitoring the temperatureinduced changes in scattering intensity, decreased significantly with increasing polymer concentration, this effect being more pronounced with decreasing polymer molar mass. In contrast, the temperature of the PNIPAM chain coil-to-globule collapse (30 ( 1 °C) was only slightly affected by solution concentration and polymer molecular weight. These results are interpreted in terms of the coexistence of two phenomena: association of the n-octadecyl terminal groups and hydration of the PNIPAM chains.