This study examines whether private disclosure on sustainability risks affects the public performance and disclosure of companies that sustainable and responsible (SRI) investors attempt to influence in hidden, behind the‐scenes dialogues. Private engagement and dialogue is the direct corporate governance mechanism of investor activism on sustainability risks prior to or independent of a shareholder resolution. A unique data set is provided by the professional agent of Nordic institutional investors for 326 private reports in relation to engagement cases trigged by environmental and social incidents in MSCI World companies. This study finds that the changes requested by Nordic SRI investors in private disclosures are, in 29.8 per cent of cases, made by the target companies. However, an initiation of private dialogue and disclosure in relation to environmental and social incidents, on average, decreases the subsequent change in market value and sustainability performance ratings of target companies in relation to a matched sample. This study finds no evidence of significant public effect of private disclosures on the target companies’ sustainability performance, sustainability transparency and financial performance in three years following an initial targeting. This study interprets empirical findings as confirming the use of private engagement and disclosure in the Nordic stakeholder model of corporate governance. The findings reveal the difficult detection of financial and sustainability outcomes of private disclosure by means of public information vehicle.