Research on the mental health effects of social networking have predominantly focused on Facebook, with limited research investigating the effects of Instagram on psychological well-being. This study aimed to address the link between Instagram use and a range of psychological variables in two parts. Participants were 129 women aged between 18 and 35 years. In Part 1, women completed a series of questionnaires related to mental health outcomes and self-perceptions. Results showed that the frequency of Instagram use is correlated with depressive symptoms, self-esteem, general and physical appearance anxiety, and body dissatisfaction and that the relationship between Instagram use and each of these variables is mediated by social comparison orientation. In Part 2, participants were exposed to a range of either beauty, fitness, or travel Instagram images (or a control condition with no images). Beauty and fitness images significantly decreased self-rated attractiveness, and the magnitude of this decrease correlated with anxiety, depressive symptoms, self-esteem, and body dissatisfaction. Therefore, excessive Instagram use may contribute to negative psychological outcomes and poor appearance-related self-perception, in line with prior research. The research has implications for interventions and education about chronic Instagram use.