Two series of single-lap, single-bolt composite joints were tested to failure in tension. The principal difference between them was the lap thickness (T). The 36 first series joints had T = 3.2 mm and the 45 second series joints had T = 6.4 mm laps. The joint layouts were defined in terms of their end distance to hole diameter (E/D) and width to hole diameter (W/D) ratios. The former ranged from 1.5 to 4 and the latter from 3 to 5. The individual and mean joint test data, presented in graphical format, comprise ultimate loads, strengths, strains and efficiencies (the latter based on ultimate strength) for the range of E/D ratios and specific W/D ratios. For the larger E/D ratios the thicker lap joints have ultimate loads about twice those of their thinner counterparts, whereas their ultimate strengths are only about 20% higher. The ultimate strains exhibit rather less clear trends, though strains up to 18000 με are achieved with large E/D and W/D ratios. The thinner lap joints have higher efficiencies (up to 36%) and the dominant failure modes (net tension and shear out) were observed in both joint series for the same E/D and W/D ratios.