A series of polymerizations of 3,6-dibromo-9-(2-ethylhexyl)carbazole was carried out in different monomer concentrations using standard Yamamoto reaction conditions. It was found that the molecular weight of the resulting poly(N-(2-ethylhexyl)carbazol-3,6-diyl) strongly depends on the monomer concentration in the reaction mixture. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) measurements confirmed the formation of low-molar-mass cyclic oligomers of the 3,6-disubstituted carbazole. In this paper we describe, for the first time, the formation of large amounts of a cyclic tetramer and of higher macrocycles in the synthesis of poly(N-alkyl-3,6-carbazoles) by the Yamamoto method. This seems to be a limiting factor in the synthesis of high molecular weight poly(N-alkyl-3,6-carbazole)s. The optical, thermal, and electrochemical properties of poly(N-(2-ethylhexyl)carbazol-3,6-diyl) have been investigated. Poly(N-(2-ethylhexyl)carbazol-3,6-diyl) is thermally stable, with 5% weight loss at 460 °C in nitrogen. The polymer exhibits a weak blue fluorescence with a maximum at 425 nm. Poly(N-(2-ethylhexyl)carbazol-3,6-diyl) is electrochemically stable, its highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels are −5.0 and −1.6 eV, respectively.