Sentinel lymph node (SLN) biopsy is an essential procedure for accurate disease staging and treatment planning in patients with melanoma and breast cancer. Conventional preoperative imaging primarily utilizes lymphoscintigraphy with technetium-99m (Tc-99m), which presents several limitations, including radiation exposure, logistical challenges, and potential delays in surgical workflow. Photoacoustic imaging (PAI) has emerged as a promising alternative, leveraging optical contrast provided by indocyanine green (ICG). A feasibility study was conducted at Erasmus MC, University Medical Center Rotterdam, to assess the potential of dual-wavelength PAI for SLN mapping. PAI was employed to perform spectroscopic measurements in healthy volunteers, supporting the development of an optimal excitation protocol. Subsequently, in the patient phase, SLN mapping was performed using PAI with ICG, and the results were compared to the standard-of-care method utilizing Tc-99m. The excitation wavelengths of 800 nm and 860 nm were selected for ratiometric imaging to effectively visualize ICG while suppressing clutter from hemoglobin and melanin. Among the eleven evaluated sentinel nodes, seven were successfully identified using PAI. The maximum SLN detection depth achieved with PAI was 22 mm. This study illustrates the feasibility of ICG-enhanced dual-wavelength PAI for preoperative SLN mapping in patients with melanoma and breast cancer, as an alternative to lymphoscintigraphy. Analysis of false-negative detections suggests improvements to PAI and optimal patient selection. The proposed ratiometric PAI methodology, compared to multiwavelength spectroscopic imaging, enables faster imaging speeds and facilitates the transition to cheaper light sources.