Small-angle X-ray scattering (SAXS) is a well known technique used for structural analysis of materials including macromolecules. In this work, we have used SAXS to measure the temporal formation of insulin oligomers, possible candidates as toxic agents in amyloid-related diseases. The X-rays form a scattering pattern which contains information on the size and shape of the samples (between 5 and 25 nm) and was first used here to characterize the native insulin system (predominantly dimeric at pH 1.6). The fits of the data using different methods (Guinier analysis and spherical model) were in good agreement and comparable with theoretical prediction. The technique was also used to deliver structural information of repeat distances and to follow the fibrillation process. Fibrillation comprises an initial lag phase, a subsequent growth step and saturation to a plateau. The results showed the formation of larger structures at the end of the oligomer process prior to fibrillation. The analysis showed good agreement with previous SANS results. In conclusion, SAXS is a useful tool for the investigation of oligomer assembly into fibrils. This process is critical to fully understand the molecular basis of amyloid-related diseases.