The titin (TTN) gene encodes the largest described protein to date and, due to its size, provides a molecular blueprint for the organisation and assembly of the muscle sarcomere (Chauveau et al., 2014). Research has demonstrated resting sarcomere length differs according to TTN isoform expression in rat skeletal muscle (Greaser and Pleitner, 2014). Differences in sarcomere length due to isoform expression may impact on muscle fascicle length, which is the primary determinant of maximal shortening velocity. Furthermore, the TTN rs10497520 polymorphism has been identified as contributing significantly to a genetic predisposition for maximal isokinetic strength at 180°∙s-1 (Thomaes et al., 2013). Consequently, the aim of this study was to investigate the potential association between the TTN rs10497520 polymorphism and muscle fascicle length in untrained, healthy Caucasian male volunteers (n = 120; age = 20.6 ± 2.3 yr; height = 1.79 ± 0.06 m; mass = 75.1 ± 10.1 kg). Resting fascicle length of the vastus lateralis muscle was assessed in vivo using B-mode ultrasound at 50% of muscle length. Identification of fascicle length was achieved by measuring the distance from fascicular origin to insertion on the aponeurosis from a single ultrasound image using digitising software. In instances where fascicles extended beyond the ultrasound field of view, extrapolation of the fascicle and aponeuroses was necessary and fascicle length was estimated. A minimum of three fascicles were measured and a mean recorded as fascicle length. Each volunteer provided either a whole blood (n = 96) or buccal cell (n = 24) sample, from which DNA was isolated and genotyped for the TTN rs10497520 polymorphism using real-time polymerase chain reaction. Chi-square analysis was completed to assess for compliance with Hardy-Weinberg equilibrium. An independent samples t-test was used to determine any genotype-dependent differences in fascicle length. Frequency of the TTN rs10497520 polymorphism was in Hardy-Weinberg equilibrium (CC = 79.2%, CT = 20.8%, TT = 0%; X2 = 1.622, P = 0.444). Vastus lateralis fascicle length was 10.6% longer in CC homozygotes than CT heterozygotes (7.3 ± 1.6 vs. 6.6 ± 1.1 cm; P = 0.036). In the absence of any TT homozygotes, reflective of the low T-allele frequency within Caucasian populations, it is unclear if fascicle length for this group would have been smaller still. Nonetheless, the results suggest that skeletal muscle fascicle length may be associated with TTN genotype, which could produce inter-individual differences in the force-velocity relationship of skeletal muscle. Replication of this report, preferably in a sample inclusive of TT homozygotes, is necessary to confirm the association of TTN genotype with skeletal muscle fascicle length.