Code:

<asp:DetailsView ID="DetailsView1" runat="server" DataSourceID="SqlDataSource_registerDetails"
                Height="50px" Width="198px" AutoGenerateRows="False" DataKeyNames="uID">
                <RowStyle Width="450px" />
                <FieldHeaderStyle Width="200px" Font-Bold="False" HorizontalAlign="Left" Wrap="True" />
                <HeaderStyle HorizontalAlign="Left" Width="200px" />
                <Fields>
                        <asp:TemplateField HeaderText="Pol">
                        <ItemTemplate>
                            <asp:Label ID="lblSex" runat="server" Text='<%# Eval("sex") %>' />
                        </ItemTemplate>
                        <EditItemTemplate>
                            <asp:DropDownList ID="ddlSex" runat="server">
                                <asp:ListItem Value="0" Text="ženski" />
                                <asp:ListItem Value="1" Text="muški" />
                            </asp:DropDownList>
                        </EditItemTemplate>
                    </asp:TemplateField>
</Fields>
            </asp:DetailsView>

Code:

If (DetailsView1.CurrentMode = DetailsViewMode.Edit) Then
Dim ddlSex As DropDownList = CType(DetailsView1.FindControl("ddlSex"), DropDownList)
Dim x = ddlSex.Items.Count
        End If