- This paper reports on a research study to investigate the wave-induced response behavior of a pair of long flexible cylinders subject to both regular and random seas. A series of large scale experiments in combination with both deterministic and probabilistic modeling techniques were used in an effort to gain a better understanding of the basic fluid/structure interaction phenomena. The large scale experiments were designed so that cylinder spacing and orientation with respect to the incident uni-directional waves could be varied. Test data were obtained which allowed the investigation of both mean-square and extreme response behavior, such as the collision of the cylinders. Comparisons between the experimental data and numerical simulations based upon a Morison equation based finite element model lead to the identification of two important mechanisms influencing the collision behavior. A probabilistic model of the collision behavior based on the first-passage formulation of a random process, accounting for the non-Gaussian nature of the response is discussed. Comparisons between non-parametric estimates from the experimental data and the probabilistic model show the importance of accounting for the non-Gaussian nature of the response in estimating the extreme response and cylinder collision behavior.