Despite prior research on portrayals of women in STEM in traditional media, fewer studies have considered portrayals on social media. This content analysis of Instagram posts ($N=300$) examined how individuals using the hashtag #WomenInSTEM presented their gender identity, STEM identity, and other social identities through digital self-portraits, selfies, and associated text. Results showed that those associating with this hashtag community primarily presented: 1) counter-gender-stereotyped portrayals, but occasionally reflected gender stereotypes in subtle ways; 2) STEM identity portrayals, mostly focused on self-recognition; and 3) self-promotional and lifestyle portrayals. Findings advance understanding of identity presentation and negotiation for individuals associating with the hashtag #WomenInSTEM through portrayals presented on Instagram. Implications for the use of social media to promote equity in STEM through outreach programs that feature women STEM role models are discussed.