Fourteen Slovak state-owned enterprises were studied, using published data and structured interviews with management. A novel methodology is used to assess SOE autonomy, effectiveness, accountability and governance. Variations in operating conditions reflect different government objectives and different ownership models. Mixed state-private firms performed more like competitive firms than did wholly state-owned SOEs. This information was fed into an assessment of Slovak SOEs’ compliance with the 2015 OECD Guidelines on SOE Corporate Governance. There are many differences between Slovak practice and the Guidelines. This may reflect a choice to favour government interests, rather than the OECD’s inclusion of a wider group of stakeholders. One cost is foregone efficiency gains. Another is the perception that the present highly opaque governance system hides corruption.